Malachi 2:2
If ye will not hear, and if ye will not lay it to heart, to give glory unto my name, saith the LORD of hosts, I will even send a curse upon you, and I will curse your blessings: yea, I have cursed them already, because ye do not lay it to heart.
The command is addressed to priests and spiritual leaders, requiring them to hear, to lay God's command to heart, and to give glory to His name. If they refuse to hear and to lay it to heart, God will send a curse upon them and will curse their blessings, and that curse is already in effect because they have not laid it to heart. The same warning states a broader principle that when people favored with light fail to honor God and obey His requirements, their blessings are turned into curses and their mercies into judgments. Having received light increases responsibility to obey, so knowing the truth yet choosing one's own way in unbelief and rebellion brings loss of God's favor and promised blessings. Israel's craving for meat despite God's warning illustrates the principle, for God granted what the people demanded but the gift came with a curse and many died, so disobedience turned blessing into judgment.
Mere profession of belonging to God is not enough, for worshipers of the true and living God must bear fruit corresponding to their light and privileges and must show the gospel's power and purity in life and good works, since empty profession misrepresents Christianity. Anything that people love and trust instead of loving the Lord and trusting wholly in Him becomes an idol and is registered as such in heaven. Human sympathies strengthened by exercise can be perverted until they become a snare, as when one is reproved for a life and character unlike Christ and others sympathize with him while overlooking the harm his wrong influence has done to God's cause. God sends His servants with a message to professed followers of Christ, but some are His children in name only and reject the warning.
The most precious blessings and most exalted privileges are prepared and promised to those who love the truth and obey it in love, but those who profess to keep the holy law while transgressing it and not living by the light given have their promised blessing changed into a curse. That curse means loss of spiritual strength and life, leaving people without spiritual vigor and moisture, dry and sapless, with only backslidden, mournful testimonies and no understanding of why.