Malachi 2:2

If ye will not hear
The commandment enjoined them; or the Gospel preached to them by Christ, and his apostles:

and if ye will not lay [it] to heart to give glory to my name,
saith the Lord of hosts;
which they had despised and profaned before; if they did not take care of his worship and service, and honour the Messiah sent unto them, in whom the name of the Lord was:

I will even send a curse upon you;
both upon priests and people; those that bring the bad offerings, and those that receive them, as Kimchi; though Abarbinel restrains it to the priests:

and I will curse your blessings,
either with which the priests blessed the people; or with which both they and the people were blessed; namely, their temporal blessings, such as their corn, and wine, and oil: and what wicked men have of this world, they have it with a curse, and not a blessing, as the righteous have; and therefore a little which they have, is better than much enjoyed by the wicked, ( Psalms 37:16 ) :

yea, I have cursed them already;
that is, from the time they began to despise his name, and not give him the glory due unto him, as Kimchi and Abarbinel explain it:

because ye do not lay [it] to heart;
to glorify God.