What does Malachi 1:12 mean?
This passage of Malachi is a condemnation of Israel's priests, for failing to bring the proper sacrifices to God. As seen in verse 10, God would prefer to see no offerings rather than apathetic or impure ones. The actions of the priests were simply the natural outcome of their attitudes, which verse 12 makes clear. Prior verses focused on the priests' failures in rituals. This passage describes their failures in relationship to God.The attitude of the priests itself is a form of disrespect to God. Even they know the correct behavior, they see proper sacrifice as too much trouble (Malachi 1:13). The effect of their mindset is described using the Hebrew word mehal'lehim', which implies a "staining," "wounding," or "polluting." In other words, God is not only being insulted, His reputation is being damaged among other people. This is as true today as it was then—when the world sees a so-called believer treating God with contempt, it demeans Him.
The New Testament will echo this error in more specific terms in James 4:17. Those who know what is right to do, and don't do it, are sinning as much as those who purposefully do evil.