I delight to do thy will, O my God: yea, thy law is within my heart.

Wesley's Notes

40:8 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.

King James Translators' Notes

within...: Heb. in the midst of my bowels

Matthew Henry's Concise Commentary

40:6-10 The psalmist foretells that work of wonder, redemption by our Lord Jesus Christ. The Substance must come, which is Christ, who must bring that glory to God, and that grace to man, which it was impossible the sacrifices should ever do. Observe the setting apart of our Lord Jesus to the work and office of Mediator. In the volume, or roll, of the book it was written of him. In the close rolls of the Divine decrees and counsel, the covenant of redemption was recorded. Also, in all the volumes of the Old Testament something was written of him, Joh 19:28. Now the purchase of our salvation is made, the proclamation is sent forth, calling us to come and accept it. It was preached freely and openly. Whoever undertook to preach the gospel of Christ, would be under great temptation to conceal it; but Christ, and those he calls to that work, are carried on in it. May we believe his testimony, trust his promise, and submit to his authority.