What does Malachi 2:12 mean?
Malachi's message is being delivered to a spiritually dead nation. The priests are apathetic and knowingly offer impure sacrifices (Malachi 1:7–8). The people are unfaithful to God (Malachi 2:11), and to each other (Malachi 1:10). One of the most serious sins being committed is marrying pagans (Malachi 2:11). This is a heinous crime in the eyes of God, because marriage is meant, in part, to symbolize the relationship between man and God. God's holiness and love can't mean much to a person willing to join with a person who rejects the truth in favor of idols.This is a serious offense, and verse 12 invokes a curse on those who commit it. To be "cut off" was a metaphor for death, either spiritual or physical. This might be a separation from the nation of Israel, or an end to that man's family line. Either way, the consequences of pagan intermarriage were severe.
Note, also, that this verse includes a jeer at the attitude of Israel. Pagan intermarriage is a clear-cut sin, and a violation of the Law. And yet, men who commit this crime have the nerve to bring offerings to God, seeking His favor. This is a sign of Israel's spiritual decay.