Proverbs 15:8-9
The sacrifice of the wicked is an abomination to the Lord,
But the prayer of the upright is His delight.
The way of the wicked is an abomination to the Lord,
But He loves him who follows righteousness.

I actually had this verse highlighted on my pc, so it must be a memorable scripture.

I have often thought about the meaning behind this verse.
Why is the sacrifice of the wicked an abomination?
It is because the sacrifice means little and does nothing. Under the Mosaic Law sacrifices took place every day because the people sinned every day and needed a covering for that sin every day. Yet, the sacrifice never completely covered and cleansed them from their sin and so the wicked are never made righteous by their sacrifice.
However, prayer gives the wicked access to the very throne of Almighty God, where that person finds mercy and grace to help in time of need.
This mercy and grace come from the blood of Jesus, which cleanses from all unrighteousness, so the wicked person is no longer wicked but made righteous.