Malachi means “messenger of Yahweh.” His main message was that the people needed to be faithful and authentic in their love for God. It ends with a hopeful anticipation of the Messiah coming to Earth. He probably wrote around 435 BC.
God promised to bless Israel, but curse the Edomites (v.4). The priests in Israel were giving the second best to God (v.8). He rejects their sacrifices (v.10). They have good sacrifices, but keep them back for themselves (v.14).
He rebukes the priests for showing partiality with the law (v.9). The people married with Pagan women (v.11).
God predicts a forerunner to his visitation of the Temple. God promises not to destroy the nation (v.6). God gives a practical insight into repenting. The people should bring their giving to him (v.10). The people were saying that following God didn’t benefit them (v.14).
God reminds them to look to the law of Moses (v.4). He promises that Elijah will return before the end (v.5). If the people reject Elijah, he will judge the people (v.6).
 Archer, Gleason. A Survey of Old Testament Introduction (3rd. ed.). Chicago: Moody Press. 1994. 478.