Abomination

Proverbs 15:8

The sacrifice of the wicked is an abomination to the Lord,
but the prayer of the upright is acceptable to him.

It is bad enough to act wickedly and ungodly and to think you can get away with bad behavior. But to feign reverence for God, to pretend to love God, or pretend to repent? God will not be mocked. And if it is possible for him to be angrier over one sin than another, be sure that his greatest anger is against those who try to drag him over to be identified with their wickedness.
There are many who profess believing the gospel, yet are filled with hate, vindictiveness, who cheat in business and school, and yet somehow justify their behavior as squaring with their faith. Their worship is received by God as an abomination.

There are others who regard themselves as upright, yet under the name of Christian undermine the gospel faith by their legalism. There are many who use the Christian pulpit to destroy confidence in God's Word. Their worship is an abomination.

God will not be mocked. He does not look with favor upon those who not only insist on going their own way, but either try to drag him along or make him conform to them. The reason the prayer of the upright is acceptable to him is that the upright conform to him. Their standard for what is righteous is what is established in God's Word. They call upon Christ, not only as Savior but as Lord.