Matthew Henry Commentary Deuteronomy 32:3-6

"For I will proclaim the name of Jehovah: Ascribe ye greatness unto our God. The Rock, his work is perfect; For all his ways are justice: A God of faithfulness and without iniquity, Just and right is he. They have dealt corruptly with him, [they are] not his children, [it is] their blemish; [They are] a perverse and crooked generation. Do ye thus requite Jehovah, O foolish people and unwise? Is not he thy father that hath bought thee? He hath made thee, and established thee." — Deuteronomy 32:3-6 (ASV)

He is a Rock. This is the first time God is called by this name in Scripture. The expression means that the Divine power, faithfulness, and love—as revealed in Christ and the gospel—form a foundation that cannot be changed or moved, on which we may build our hopes for happiness.

Under His protection, we may find refuge from all our enemies and in all our troubles, just as rocks in those lands provided shelter from the burning rays of the sun and from tempests, or served as fortresses against the enemy.

His work is perfect: this refers to the work of redemption and salvation, in which there is a display of all the Divine perfection, complete in all its parts.

All God's dealings with His creatures are regulated by wisdom that cannot err and by perfect justice. He is indeed just and right; He ensures that no one will suffer loss because of Him.

A serious charge is brought against Israel. Even God's children have their spots while in this imperfect state; for if we say we have no sin, no spot, we deceive ourselves.

But the sin of Israel was not habitual, notorious, unrepented sin, which is a certain mark of the children of Satan. They were fools to forsake their mercies for lying vanities. All willful sinners, especially sinners in Israel, are unwise and ungrateful.