Malachi 3:6

the Lord--Jehovah: a name implying His immutable faithfulness in fulfilling His promises: the covenant name of God to the Jews (Exo 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. Rom 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" (Gen 28:13; Gen 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 (Lam 3:22) into a ground for skeptical denial of His coming as a Judge at all (Psa 50:1, Psa 50:3-4, Psa 50:21; Ecc 8:11-12; Isa 57:11; Rom 2:4-10).

For I am the Lord,.... Or Jehovah; a name peculiar to the most High, and so a proof of the deity of Christ, who here speaks; and is expressive of his being; of his self-existence; of his purity and simplicity; of his immensity and infinity; and of his eternity and sovereignty: I change not; being the same today, yesterday, and forever; he changed not in his divine nature and personality by becoming man; he took that into union with him he had not before, but remained the same he ever was; nor did he change in his threatenings of destruction to the Jews, which came upon them according to his word; nor in his promises of his Spirit, and presence, and protection to his people; nor will he ever change in his love and affections to them; nor in the efficacy of his blood, sacrifice, and righteousness; wherefore, as this is introduced to assure the truth and certainty of what is said before, concerning his being a swift witness against the wicked, so also for the comfort of the saints, as follows. The Targum is, "for I the Lord have not changed my covenant.'' Therefore ye sons of Jacob are not consumed; such who were Israelites indeed, true believers in Christ; these were not consumed when the wicked Jews were, but were directed to leave the city before its destruction, and go to another place, as they did, whereby they were preserved; and so it was, that not one Christian perished in it; See Gill on Mat 24:13 and so it is owing to the unchangeable love, grace, and power of Christ, that none of his perish internally or eternally, but have everlasting life.

Coming of the Lord to judgment. Mal 3:1. "Behold, I send my messenger, that he may prepare the way before me; and the Lord, whom ye seek, will suddenly come to His temple, and the angel of the covenant, whom ye desire; behold he comes, saith Jehovah of hosts." To the question, Where is or remains the God of judgment? the Lord Himself replies that He will suddenly come to His temple, but that before His coming He will send a messenger to prepare the way for Him. The announcement of this messenger rests upon the prophecy in Isa 40:3., as the expression וּפנּה דרך, which is borrowed from that passage, clearly shows. The person whose voice Isaiah heard calling to make the way of Jehovah in the desert, that the glory of the Lord might be revealed to all flesh, is here described as מלאך, whom Jehovah will send before Him, i.e., before His coming. This maleâkh is not a heavenly messenger, or spiritual being (Rashi, Kimchi), nor the angel of Jehovah κατ ̓ ἐξοχήν, who is mentioned afterwards and called maleakh habberı̄th, but an earthly messenger of the Lord, and indeed the same who is called the prophet Elijah in Mal 4:5, and therefore not "an ideal person, viz., the whole choir of divine messengers, who are to prepare the way for the coming of salvation, and open the door for the future grace" (Hengst.), but a concrete personality - a messenger who was really sent to the nation in John the Baptist immediately before the coming of the Lord. The idea view is precluded not only by the historical fact, that not a single prophet arose in Israel during the whole period between Malachi and John, but also by the context of the passage before us, according to which the sending of the messenger was to take place immediately before the coming of the Lord to His temple. It is true that…

In this chapter we have, I. A promise of the coming of the Messiah, and of his forerunner; and the errand he comes upon is here particularly described, both the comfort which his coming brings to his church and people and the terror which it will bring to the wicked (Mal 3:1-6). II. A reproof of the Jews for their corrupting God's ordinances and sacrilegiously robbing him of his dues, with a charge to them to amend this matter, and a promise that, if they did, God would return in mercy to them (Mal 3:7-12). III. A description of the wickedness of the wicked that speak against God (Mal 3:13-15), and of the righteousness of the righteous that speak for him, with the precious promises made to them (Mal 3:16-18).

3:6-12 Malachi’s fifth message echoes the first (1:2-5) by emphasizing God’s faithfulness to his promises. He calls Israel to a similar faithfulness in worship, especially in giving their tithes and offerings. If Malachi is a courtroom drama, the fifth message is the judge’s verdict. The real message is repentance—God wants honest and sincere worship from his people, of which tithing is a symbol.