John Calvin Commentary Deuteronomy 28:63

"And it shall come to pass, that, as Jehovah rejoiced over you to do you good, and to multiply you, so Jehovah will rejoice over you to cause you to perish, and to destroy you; and ye shall be plucked from off the land whither thou goest in to possess it." — Deuteronomy 28:63 (ASV)

And it shall come to pass, that as the Lord rejoiced over you. The wonderful and inestimable love of God toward His people is here set forth, namely, that He had rejoiced in heaping blessings upon them; therefore, their depravity was all the more despicable and intolerable, because God, though voluntarily disposed to be bountiful, was compelled by it to lay aside His affection for them.

But although it is only by a metaphor that God is said to rejoice in destroying the wicked, yet it is not without good reason that this expression is applied to Him, so that we may know that He can no more fail to be the defender of His Law and the Avenger of its contempt than He can deny Himself.

He complains, indeed, through Isaiah (Isaiah 10:24) that He is unwillingly forced to punish the Jews; but these two things are quite consistent: that He rejoices in His just judgment and, at the same time, is mindful of His clemency and indulgence, so that He would rather pardon if the wickedness of men would allow Him. But this expression of Moses—that God receives consolation from punishing the wicked—constantly occurs in the Prophets.