The Book of Malachi is written in diatribe style, the purpose of which is to exhort and admonish both priests and people to embrace and do the will of God. The book was written during the post-exilic period, after the return from Babylon which occurred in 538 BC, and after the construction of the temple (circa 518 BC) but (according to some scholars) before the return of Ezra, whose date of return is disputed. The NABRE suggests the book was written around 445 BC, after the return of Ezra but just before the return of Nehemiah.
The work contains six diatribes, with the first providing the foundation for the rest: 1. God loves Israel and wishes to maintain covenant relations with his people (Mal 1:2-5). 2. For this relationship to continue the priests must offer proper sacrifices at the temple (Mal 1:6-2:9). 3. The people must maintain their marriages as if safeguarding their own lives (Mal 2:10-16). 4. God will send a messenger of righteousness to refine the people (i.e., make them repentant) before He returns in judgment (Mal 2:17-3:5). 5. God, through His prophet, exhorts the people to offer tithes that are not fraudulent. If they try this they will find blessing (Mal 3:6-12). 6. Exhortations and warning to remember the covenant (Mal 3:13-4:5 [i3:13-24 in NABRE]).
FIRST DIATRIBE, Mal 1:2-5. After a brief superscription (Mal 1:1) the body of the book opens with its first diatribe which is directed against those who say and act as if God doesn’t love them. But God insists that His love is manifested by the fact that He chose their father Jacob (also called Israel) rather than his brother Esua (father of the Edomites). By the time of Malachi the People of God had been exiled, their land destroyed; but they had returned and rebuilt. The country of Edom was desolate and would never be rebuilt.
Proof of God’s love for his people is the point of this first diatribe and it establishes the basis for all the rest. Further, each subsequent diatribe prepares for the one following it, or, is related to the one preceding it.
SECOND DIATRIBE, Mal 1:6-2:9. Because of his abiding love (first diatribe) God deserves from the priests the honor due a father, and reverential fear due to a master. But the priests have begun offering impure and sick animals which even the pagan governor then ruling over the land would not be pleased with (Mal 1:7-8). Thus–and this calls to mind the first diatribe–they are shown treating with contempt the God who chose them (Jacob) over pagan peoples (Esau). The prophet looks forward to a time when God’s name will be great and feared among the nations and a pure sacrifice will be continually offered to Him (Mal 1:11, 14).
THIRD DIATRIBE, Mal 2:10-16. Just as the priests have broken the covenant with Levi and profaned the Temple (second diatribe), so too have the men of Judah broken the covenant of the fathers and defiled the sanctuary, here possibly referring to the legitimate wife as a temple (Mal 2:10-11). this they have done by breaking the marriage covenant with their wives to marry the daughters of foreign gods. (Mal 2:14-16). The Lord desires Godly offspring (Mal 2:15).
FOURTH DIATRIBE, Mal 2:17-3:5. The God who hates divorce and desires Godly offspring (third diatribe) is a God who demands justice among people (Mal 2:17). He will purify those who have broken the covenant with Levi (Mal 3:3-4, referring to diatribe 2); and He will judge those who deal wickedly, especially those guilty of perverting marriage (adulterers), and those who oppress people who have lost their family (widows and orphans, Mal 3:5).
FIFTH DIATRIBE, Mal 3:6-12. The God of justice who always seeks to bring His people to repentance and judges those who refuse (fourth diatribe) does not change, and this keeps His people from being consumed (Mal 3:6). Thus God challenges His people to challenge Him, put Him to the test by offering tithes rightly, then they will see Him fulfill His covenant promises (Mal 3:10-12, see Deut 28:1-15).
SIXTH DIATRIBE: Mal 3:13-4:6 [3:13-24 in NABRE]. The God who challenged His people to challenge Him (fifth diatribe) now critiques those who say that the wicked prosper when they put God to the test (Mal 3:13-15). By divine judgement those who heed the Lord will be distinguished from those who do not (Mal 3:16-4:3). The Lord who promised not to destroy the fruit of the soil and the abundance of the fields if His people responded to him (fifth diatribe), ends His last diatribe by telling His people to remember the Covenant with Moses, and assures them that He will send them Elijah to preach repentance, “lest I come and smite the land with a curse” (Mal 4:5-6).
In my opinion the first three diatribes parallel sequentially the second three (note the color coding).
The book began by emphasizing the fact that God had specially chosen Jacob (Israel) over Esau (Edomites); and it highlighted the fact that the land of the latter had been thoroughly destroyed (Mal 1:2-5). The book ends with the Lord distinguishing between the righteous and the wicked; between those who serve God and those who don’t; and a warning is given to repent, lest God smite the land with an Edom-like curse (Mal 3:13-4:5). The lesson here is quite simple: you cannot treat being chosen by God as if it were a cheap gift. Every one to whom much is given, of him will much be required (Lk 12:48). You are a chosen race, a royal priesthood, a holy nation, God’s own people (1 Pet 2:9), and it is for this very reason that it is imperative to understand that judgement begins with the household of God (1 Pet 4:17). God’s grace and favor bring great responsibilities: You only have I known of all the families of the earth; therefore I will punish you for all your iniquities (Amos 3:2)