For I am the LORD, I change not; therefore ye sons of Jacob {f} are not consumed.

(f) They murmured against God, because they did not see his help which was ever present to defend them: and therefore he accuses them of ingratitude, and shows that in that they are not daily consumed, it is a sign that he still defends them, and so his mercy towards them never changes.

Wesley's Notes

3:6 I change not - I have an unchangeable hatred to sin: and my long suffering also changeth not, therefore you are not consumed in your sins. Not consumed - God is the same in his wisdom to order the rewards of good and bad in the fittest season, therefore neither the one nor the other are consumed, but preserved to the season appointed of God.

Jamieson-Fausset-Brown Bible Commentary

6. the Lord-Jehovah: a name implying His immutable faithfulness in fulfilling His promises: the covenant name of God to the Jews (Ex 6:3), called here "the sons of Jacob," in reference to God's covenant with that patriarch.

I change not-Ye are mistaken in inferring that, because I have not yet executed judgment on the wicked, I am changed from what I once was, namely, a God of judgment.

therefore ye . are not consumed-Ye yourselves being "not consumed," as ye have long ago deserved, are a signal proof of My unchangeableness. Ro 11:29: compare the whole chapter, in which God's mercy in store for Israel is made wholly to flow from God's unchanging faithfulness to His own covenant of love. So here, as is implied by the phrase "sons of Jacob" (Ge 28:13; 35:12). They are spared because I am Jehovah, and they sons of Jacob; while I spare them, I will also punish them; and while I punish them, I will not wholly consume them. The unchangeableness of God is the sheet-anchor of the Church. The perseverance of the saints is guaranteed, not by their unchangeable love to God, but by His unchangeable love to them, and His eternal purpose and promise in Christ Jesus [Moore]. He upbraids their ingratitude that they turn His very long-suffering (La 3:22) into a ground for skeptical denial of His coming as a Judge at all (Ps 50:1, 3, 4, 21; Ec 8:11, 12; Isa 57:11; Ro 2:4-10).

Matthew Henry's Concise Commentary

3:1-6 The first words of this chapter seem an answer to the scoffers of those days. Here is a prophecy of the appearing of John the Baptist. He is Christ's harbinger. He shall prepare the way before him, by calling men to repentance. The Messiah had been long called, He that should come, and now shortly he will come. He is the Messenger of the covenant. Those who seek Jesus, shall find pleasure in him, often when not looked for. The Lord Jesus, prepares the sinner's heart to be his temple, by the ministry of his word and the convictions of his Spirit, and he enters it as the Messenger of peace and consolation. No hypocrite or formalist can endure his doctrine, or stand before his tribunal. Christ came to distinguish men, to separate between the precious and the vile. He shall sit as a Refiner. Christ, by his gospel, shall purify and reform his church, and by his Spirit working with it, shall regenerate and cleanse souls. He will take away the dross found in them. He will separate their corruptions, which render their faculties worthless and useless. The believer needs not fear the fiery trial of afflictions and temptations, by which the Saviour refines his gold. He will take care it is not more intense or longer than is needful for his good; and this trial will end far otherwise than that of the wicked. Christ will, by interceding for them, make them accepted. Where no fear of God is, no good is to be expected. Evil pursues sinners. God is unchangeable. And though the sentence against evil works be not executed speedily, yet it will be executed; the Lord is as much an enemy to sin as ever. We may all apply this to ourselves. Because we have to do with a God that changes not, therefore it is that we are not consumed; because his compassions fail not.