The context of this instruction is that of defiled sacrifices and a defiled priesthood. From Malachi 1:6 we learn that offering defiled sacrifices caused God’s name to be defiled. From Malachi 1:12 we learn that by offering profane sacrifices, they profaned God’s name. What we offer to God is a reflection of how we regard God. If we regard God pure and perfect in every way, we will offer what is pure and perfect. By such offerings, God’s name is glorified. But if we think less of God, we will offer what is less that pure and perfect. By accepting blemished, second-grade offerings, the priests showed their low regard for God, causing his name to be profaned.
2 If you will not listen, if you will not take it to heart to give honor to my name, says the LORD of hosts, then I will send the curse upon you and I will curse your blessings. Indeed, I have already cursed them, because you do not lay it to heart.