What are the true motives for holiness? - D. Martyn Lloyd-Jones

“Let not sin therefore reign in your mortal body, to make you obey its passions. Do not present your members to sin as instruments for unrighteousness, but present yourselves to God as those who have been brought from death to life, and your members to God as instruments for righteousness. For sin will have no dominion over you, since you are not under law but under grace.” Romans 6:12-14

“Do you long to be holy? Do you long to have victory over sin in your mortal body? How can you do so? First, understand the doctrine. You cannot work out ‘therefore’ unless you are clear about the doctrine…Understanding the doctrine – that is the place to start. You must not say ‘I am not interested in doctrine; all I do is to look to Christ & allow Him to live His life in me’. The ‘therefore’ insists that you must understand the doctrine. Then, having understood it, you must remind yourself of it constantly. ‘Reckon’ – go on reckoning, keep on reckoning, realize it, apply it to yourself, & then draw the inevitable deductions from it…
What are the true motives for holiness? They are not just a reaction against the evil nature of sin, they are not just the desire to be happy. These are a part of it, but not the chief motive. Still less should we seek to be holy in order to make ourselves Christians; & still less merely because we are afraid of hell & the punishment of hell. Our motives must be entirely positive. Why must I not allow sin to reign in my mortal body? Because I am a man who claims to know what God’s purpose is for me. And what is God’s purpose for me? It is that all the works of the devil shall be undone in me. God made me in His own image, He made me perfect; & His whole purpose in salvation is to bring me back to that state. I believe that, I know that, I realize that; therefore I cannot allow sin to reign in my mortal body. That is my motive. I know what God’s purpose for me is, & all He has planned, & all He has brought to pass. That is my grand motive, but there are others.
I know what the Lord Jesus Christ has done for me. Knowing this doctrine, I believe that the second Person in the blessed holy Trinity left the courts of heaven & came into this world, & not only lived as a man but humbled Himself so as to come in the likeness of sinful flesh. I believe that He went to Calvary & bore my sins in His own body on the tree, & suffered the agony & the indignity of it all for me. Why did He do all that? That we might continue in sin? No! but ‘that He might redeem us from all iniquity & purify unto Himself a peculiar people zealous of good works’ (Titus 2:14). So how can we go on with sin?
These are the motives, this is the way in which I become sanctified. It is because I know these things that I will not allow sin to reign in my mortal body. I therefore go on to draw this deduction, that the very honour of God, & of the Lord Jesus Christ, is involved in this matter of my behavior…
It is the truth that sanctifies: ‘You shall know the truth & the truth shall make you free’, said our Lord to the people (John 8:32). The truth that makes us free is that which tells us who we are, what we are, what has been done for us, & how the whole honour of the family is, as it were, in our hands.”

- Martyn Llloyd-Jones, Exposition of Romans Chapter 6: The New Man