Perhaps most unexpected of the answers the LORD gives to Malachi is this:
This also you do: the altar of the LORD you cover with tears, weeping and groaning, Because he no longer regards your sacrifice nor accepts it favorably from your hand; and you say, "Why is it?"-- Because the LORD is witness between you and the wife of your youth, With whom you have broken faith though she is your companion, your betrothed wife.
Our sacrifice is no longer accepted favorably, not just because we've broken faith with the wife of our youth. Of course we're sinners. That's what the sin offerings are for.
But God rejects our sacrifices because He was the witness of our marriage.
What does our marriage back before have to do with our sacrifice here today? Everything, when you're dealing with a God Who Is by nature a relationship of persons.
We invited God to witness our marriage, and He saw what He saw. Now we come along, having broken faith with our companion, expecting Him to unsee what He saw, even as we ask Him to see our sacrifice today.
"Who are You going to believe," we ask the LORD with tears, weeping and groaning. "Me, or Your own lying eyes?"