I am, therefore I do.
Our reading from Romans 12 starts with:

Therefore, I urge you, brothers, in view of God’s mercy, to offer your bodies as living sacrifices, holy and pleasing to God – this is your spiritual act of worship.

Most of us “know” Romans 12, verses 1 to 8 almost by heart.  In fact, when you’ve heard them repeatedly, ad nauseum, you actually switch off and stop paying attention. You think you already know it.
I’m always busy skimming ahead, searching for the “quick fix instructions”:  how to live a better Christian life? What do I have to DO?
And so, I jump over the first phrase “in view of God’s mercy” and I boldly grasp hold of “offer your bodies as living sacrifices, holy & pleasing to God”.  That’s the “what I’m supposed to do” – alright! let’s do it!
What’s interesting to note is that most of Paul’s teaching (I read this somewhere – and I’m amazed it actually stuck in my mind), the books of Romans, Corinthians, Galatians, Ephesians, & Colossians – all seem to be divided in 2 halves.
First half: Theology. God’s character or what Christ is or has done.
Second half: Christian behaviour – what to do. What to avoid.
Part I – answers the question: WHY?
Part II – answers the question: HOW?
Finally – the explanation of why I always enjoy the 2nd half of his writing much more than the first half.
If you look in my study Bible, you will find Galatians 5 & 6 heavily studied, while chapters 1 to 4 are hardly touched; the Mary’s of this congregation will enjoy Ephesians chapters 1 to 3 for study, meditation and prayer – and I’m sure that like me the Martha’s skip over those and go straight to chapters 4, 5 & 6 – where almost every single verse will give you instructions about what to do to be a better Christian.  You might also read Colossians 2, onward – where is says “continue to live in Christ, rooted and built up in Him”, you will be tempted to skip over Paul’s’ discussion of the Supremacy of Christ in chapter 1 and the beginning of Chapter 2…
My study Bible divides Romans in 2 parts: Chapters 1 to 11 (Part A – actually titled  – “What to Believe”) and Chapter 12 to the end (Part B – “How to Behave”).  ¿Notice how part A is always so much longer than part B?
And so, I skip over the reference in verse 1 of Romans 12 to God’s mercy (perhaps not having understood it, because Romans 11 just seems so dry… I mean, have you read it?  “The remnant of Israel”;  “ingrafted branches” and “all Israel will be saved”).  Come on Paul! Just get to the point!  What are we supposed to be doing here?
Of course, Paul DOES actually explain the importance of “what to believe”, in order to tell us “how to behave”.

Romans 12: 2 – … be transformed by the renewing of your mind. THEN you will be able to test and approve what God’s will is – His good, pleasing & perfect will.

The more I know God (and know “what to believe”), the better I understand the Creator, and the better I understand God, the more I am able to think like God, and the more I think like God, I am able to discern His will for me and my life.  And THEN I will know what to do!

So, Paul starts this Part B “How to Behave”, with a reference to Part A – what to believe (how to think). And this reference is “in view of God’s mercy”.
What mercy?
Well, the mercy he’s been talking about for the last 11 chapters of Romans that you skipped over because it’s oh… soo…  a little dry, perhaps?
Here’s your 20-second summary of chapters 1 to 11:  the foundations of Christian holiness & righteousness.  God is gracious and gives us a free gift of righteousness that we don’t deserve.  In faith, we believe in the Lordship of God and in His loving mercy to save us and count us as righteous through Christ.
Maybe a little too precise!
Let’s try the 1-minute summary:
Romans 1, 2 & 3 – You’re all a bunch of sinners.
Romans 4 & 5 – Not to worry, God did something about it.
Romans 6 – We identify with Christ in baptism, likening this to death, leaving our “old self” behind and being renewed into a new self.  Old self is dead.
Romans 7 – occasionally, however, the old self comes back to bite me, and as much as I try to be well-behaved and do what I’m supposed to, I keep messing it up. Woe is me! What a wretched man I am!  Oh… but that’s right, I’m not the one that’s supposed to be doing the work of transformation.
Romans 8 – the Holy Spirit is supposed to transform me – stop trying so hard to do it yourself and let God be God.
Romans 9, 10 & 11 – God’s plan of salvation isn’t limited to the Hebrew nation, but also the Gentiles.  God understands that man is sinful, but is gracious & merciful, and is going to take care of the salvation of man, because whatever man does will never be good enough.

God’s mercy for mankind is that man can re-establish the relationship with God and spend eternity in God’s presence, light and love.
So, there you have it – God is merciful & gracious.  That should be enough of an explanation to take care of the neuro-part of changing your way of acting.  Right?

I haven’t even begun to comprehend God’s mercy, but I see it best in the Old Testament:  Welcome to the bullet train ride, through Genesis to Judges in less than 5 minutes!
God and the angels are all in heaven.  Satan decides he’s the most beautiful creature ever created, and gets 1/3 of the angels to believe him.  They revolt against God – demanding an independent democracy, 2-party system, with elections every 5 years and the right to be re-elected.  God unilaterally overrules their motion, Satan and the fallen angels are banished from heaven.
God creates the heavens, earth, and light; sky, brings up dry land, and gets vegetation to grow on the land; creates the stars, sun & moon; creates the creatures of the sea, birds, and animals, livestock, etc., and then makes his masterpiece – man in his own image.  He gives man dominion over the living creatures.
Satan is jealous – why didn’t he get one of those worlds?
God sees that man is lonely, and so makes a woman for him.
Satan’s really jealous now!
Then Satan sees opportunity: a chance to get more power and followers.  He tricks the woman into disobeying God, seeking to become like God herself – and Adam with her.
Ha! Got them!  Commit the very same sin for which Satan had been banished:  man gets banished from the Garden of Eden.  Satan’s elated –if you can’t rise to the challenge, bring them down to your level.
But God, in His great mercy, keeps His Word and yet manages to re-establish his relationship with man, by sacrifices of innocent blood of a lamb:
Cain & Abel, the gardener and the shepherd, make their offerings to God.  Cain gets angry and hurt when God favours Abel’s offering, and kills his brother.  Rather than killing Cain, God in his mercy marks him with a special mark, so that others will not kill him.
God establishes a special friendship with Abram, and promises him that his descendants will occupy Canaan.  They move to Egypt because of the famine, and there they grow and multiply, but because the Pharaoh is scared of them, he makes them into slaves.  God, in His mercy, hears their cries and remembers his promise to Abram, and sends Moses to lead them out of Egypt.
When getting out of Egypt proves a little harder than just telling Pharaoh to let them go, and Pharaoh orders harder labour, the Israelites complain against Moses & Aaron. Satan starts smiling, opportunity knocks… where there’s complaining there is rebellion and sedition.
After 10 plagues on Egypt and more hardship, Pharaoh tells them all to leave and get out, and God is merciful and gracious: the people of Egypt gave them all their articles of gold and silver.
They camp by the Red Sea and Pharaoh chases after them.  The Israelites are terrified and complain to Moses – Did you bring us to the desert to die?  But God is merciful, and delivers them from the Pharaoh and his army, and they celebrate with songs and dance.
3 days later and the water in Marah is bitter, so they grumble to Moses “why isn’t everything perfect? I’m a Christian – I shouldn’t have any problems”. God is merciful, and shows Moses a piece of wood, to make the water sweet.
After 6 weeks of travel, they start to grumble and complain – they have no food. God, in His great mercy, rains down manna from heaven.  They get bored with the manna, “Rice & beans with sardines, again? Back in Egypt we had McDonalds, SushiExpress, vegetarian delights, and Italian cuisine”, and oh… how they complain, but God, in His mercy, gives them quail to eat.
They reach the Desert of Sin: no water, they complain… and God, in His mercy, tells Moses to strike the rock and water gushes forth.
Because there are 600,000 men as well as women & children, God gives Moses the 10 commandments and some other rules.  In the 40 days Moses is up on Mount Sinai, the children of Israel get impatient, the complain… Moses obviously isn’t coming back and they make a golden calf. Satan throws a massive party!
God suggests to Moses that He will destroy them all, but Moses reminds God of His promises to Abram, and so God relents and is merciful.  They get the 10 commandments on the tablets of stone.
When they get to the Promised Land, the 10 spies forget that their mission was to tell the people HOW to invade Canaan, and suggest that they shouldn’t even try.  Forget everything that God has done so far! All those miracles, they’re worthless.  Not near strong enough to defeat these giants!
They complain and rebel against Moses.  God threatens to destroy them all.  Moses reminds God of His promises, and God in his mercy does not strike them all dead.  Instead, He forgives them, but removes the GPS unit from the camels and so they wander the desert for 40 years, with a little complaining and a few rebellions along the way.

You can almost HEAR the women saying “I told you to stop and ask for directions, but no… you’re not lost… which is why we’ve run into this same oasis 3 times in the last 8 years. No… we’re not going around in circles!  Men! We could have asked those Bedouins for directions and been there already.”
Joshua leads them victoriously into the Promised Land.  They take Jericho by the power of God, with the walls miraculously crumbling down.  But, as we always do when faced with a seemingly normal situation, when the Gibeonites come to them demanding peace, they forget to ask God’s opinion and made a treaty. When they discover they’ve been tricked, it was too late.
Oops.
Nonetheless, God, in His mercy, still helps them to conquer all of the land that they were promised.
Once they were settled into the Promised Land, they became complacent, and failed to drive out all the remaining peoples. Satan re-establishes his residence in the high-places.  God appears at Bokim, reminding them of the covenant He had made with them “I will never break my covenant with you, and you shall not make a covenant with the people of this land, but you shall break down their altars.”  But the people of Israel had disobeyed. They repented and God, in His mercy, accepted their sacrifices and forgave them.
A new generation was born, that didn’t know personally what God had done for Israel, and they started to worship Baal and other gods of the people around them.
God allows other nations to raid their lands and plunder it.  But God, in His great mercy, raised up judges who saved them out of the hands of these raiders.  But they didn’t always listen to the judges, and quickly turned to worshipping other gods.  Whenever God raised up a judge, he was the judge and saved them out of the hands of their enemies as long as he lived, because God had compassion on them as they groaned under those who oppressed and afflicted them.  But when the judge died, the children of Israel would forget God and go back to following other gods.

God in His mercy and grace eventually sends Jesus as the ultimate sacrifice, Satan’s ecstatic when the Jews send Jesus to be crucified on the cross!   When it’s too late, Satan realises that God had an ulterior plan, taking the battle right down into the depths of hell to beat Satan on his own ground, and raising Jesus from the dead.
Never quite seems to work out for him!  God somehow manages to play by the rules and still win! It’s just not fair!
And because the Israelites failed to accept Christ, salvation comes to the Gentiles as well.
By faith in God & His mercy, anyone can re-establish the relationship with God.
And so we read in Romans 11, verses 33 to 36:

Oh, the depth of the riches of the wisdom and knowledge of God!  How unsearchable His judgements, and His paths beyond tracing out!  Who has known the mind of the Lord?  Or who has been His counsellor?  Who has ever given to God, that God should repay Him?  For from Him and through Him and to Him are all things. To Him be the glory…

So, there, I’ve said it.  God’s great mercy and grace is simply this –we can accept His transformation by the renewing of our mind, by the simple act of believing, changing our perspective of how we view ourselves.
Forget about that Romans 7 man or woman, the “sinner” – defeated – unworthy.  Of course you can’t fulfil the law!
See yourself through God’s eyes – the potential of what you COULD become if you allowed GOD to transform and change you.  Don’t focus on what you are right now, on your failures and weaknesses of the past.  Live in the present, today, and look to your future – be transformed by the renewing of your mind.

I’d like to finish today, by reading Romans 12, verses 1 to 8, to you, remembering God’s great mercy. This is from the version “The Message”.
So, here’s what I want you to do, God helping you:
Take your everyday, ordinary life – your sleeping, eating, going-to-work, and walking around life – and place it before God as an offering.  Embracing what God does for you is the best thing you can do for him.
Don’t become so well-adjusted to your culture that you fit into it without even thinking.  Instead, fix your attention on God.  You’ll be changed from the inside out.
Readily recognise what He wants from you, and quickly respond to it.  Unlike the culture around you, always dragging you down to its level of immaturity, God brings the best out of you, develops well-formed maturity in you.
I’m speaking to you out of deep gratitude for all that God has given me, and especially as I have responsibilities in relation to you.
Living then, as every one of you does, in pure grace, it’s important that you not misinterpret yourselves as people who are bringing this goodness to God.  No, God brings it all to you.
The only way to understand ourselves is by what God is and by what He does for us, not by what we are and what we do for Him.
In this way, we are like the various parts of a human body.  Each part gets its meaning from the body as a whole, not the other way around.  The body we’re talking about is Christ’s body of chosen people.  Each of us finds our meaning and function as a part of His body.  But as a chopped-off finger or cut-off toe we wouldn’t amount to much, would we?  So since we find ourselves fashioned into all these excellently formed and marvellously functioning parts in Christ’s body, let’s just go ahead and be what we were made to be, without enviously or pridefully comparing ourselves with each other, or trying to be something we aren’t.
If you preach, just preach God’s Message, nothing else; if you help, just help, don’t take over; if you teach, stick to your teaching; if you give encouraging guidance, be careful that you don’t get bossy; if you’re put in charge, don’t manipulate; if you’re called to give aid to people in distress, keep your eyes open and be quick to respond; if you work with the disadvantages, don’t let yourself get irritated with them or depressed by them.  Keep a smile on your face.

Like it says above:
The only way to understand ourselves is by what God is and by what He does for us, not by what we are and what we do for Him.
The more I know God (and know “what to believe”), the better I understand the Creator, and the better I understand God, the more I am able to think like God, and the more I think like God, I am able to discern His will for me and my life.  I recognise my gifts – And THEN I know what to do!

Now go out – by God’s mercy – and serve others as you were meant to!