What does Malachi 2:1 mean?

The entire first portion of Malachi has been directed at the priests. These men were supposed to be the messengers and teachers of God's truth to Israel. Instead, they have sneered at the truth and treated proper sacrifices as though they were too much trouble (Malachi 1:13). The situation had deteriorated to the point where priests were sacrificing animals so flawed that other people would not have accepted them (Malachi 1:8). The people were promising one thing and delivering something else (Malachi 1:14). In response, God says that He would prefer they stop offering any sacrifices at all, instead of insulting Him with lazy, arrogant rituals (Malachi 1:10).

This verse adds great emphasis to the fact that God is speaking directly to the priests. What comes after is not a "command," in the sense of a set of directions, but a warning based on their past sins. This warning is meant to be taken as an instruction to correct the situation. The next few verses describe a "curse" God will bring on the priesthood if they do not change their ways. In particular, this threat involves their humiliation, disgrace, and confusion.