I delight to do thy will, O my God - To wit, in obeying the law; in submitting to all the trials appointed to me; in making an atonement for the sins of men. See the notes at Hebrews 10:7. Compare Philippians 2:8; Matthew 26:39.
Yea, thy law is within my heart - Margin, "In the midst of my bowels." So the Hebrew. The idea is, that the law of God was within him. His obedience was not external, but proceeded from the heart. How true this was of the Redeemer it is not necessary here to say.

To do thy will - God willed not the sacrifices under the law, but he willed that a human victim of infinite merit should be offered for the redemption of mankind. That there might be such a victim, a body was prepared for the eternal Logos, and in that body he came to do the will of God; that is, to suffer and die for the sins of the world.
1. Hence we see that the sovereign Will of God is that Jesus should be incarnated; that he should suffer and die; or, in the apostle's words, taste death for every man; that all should believe on him, and be saved from their sins; for this is the Will of God, our sanctification.
2. And as the apostle grounds this on the words of the Psalm, we see that it is the Will of God that that system shall end; for as the essence of it is contained in its sacrifices, and God says he will not have these, and has appointed the Messiah to do his will, i.e., to die for men, hence it necessarily follows, from the psalmist himself, that the introduction of the Messiah into the world is the abolition of the law; and that his sacrifice is that which shall last for ever.

I delight to do thy will, O my God,.... This he came down from heaven to do, and this he did do, by preaching the Gospel, and working miracles; and above all by obtaining eternal redemption for his people, which he effected by fulfilling the law, becoming a sacrifice, and suffering and dying in their room; all which were the will of God, and grateful to him, and in doing which Christ took the utmost delight and pleasure, John 4:34;
yea, thy law is within my heart; either the whole moral law, under which he was, as man, and the surety of his people; and which was written upon his heart, and which he perfectly obeyed; or that particular law, injunction, and command laid upon him by his Father, to offer himself a sacrifice, and lay down his life for men; which he agreed to, had it in his mind, his heart was set upon it, and he cheerfully complied with it, John 10:18.

I delight - This is eminently true, of Christ, and is here observed as an act of heroic obedience, that he not only resolved to do, but delighted in doing the will of God, or what God had commanded him, which was to die, and that a most shameful, and painful, and cursed death. My heart - I do not only understand it, but receive it with heartiest love, delighting both to meditate of it, and to yield obedience to it.