Malachi is concerned about breaking faith. He draws the connection between the sense that the people have of God, and the way that they react to God and treat each other.
He identifies their treacherous attitudes, their ignorance of the impact of God as covenant Father and gracious Creator of a chosen community, holy and pure, and the way that it impacts upon their treatment of each other.
He specifies their treacherous marriages, taking idolaters as spouses and so disdaining God and damaging their identity as God's people. God will cut off from his people those who pursue such a course.
Then there are their treacherous divorces, abandoning the wives of their youth in acts of violent betrayal, which God hates and against which he will bear a fierce witness. Because of this, those who are God's should take heed to their souls.
All along the way, we trace out some of the parallels between the Old Testament community of Israel and the New Testament church of Christ.