Too often this phrase is used in vain because its purveyors have absolutely no understanding of what it means.
It comes from Ephesians 4:32 where Paul explains why God has forgiven us.
This is very different than the offer of conditional forgiveness to Israel found in Matthew 6:14-15.
Before the mystery of the cross was revealed to Paul forgiveness came to Israel only if they forgave others. Their forgiveness was conditional to their obedience.
Our forgiveness in the dispensation of grace has nothing to do with our obedience or disobedience!
Romans 4:5 forbids works for righteousness and God justifies the ungodly when we put our faith in what Christ did on the cross.
Paul tells us that we Gentiles were without Christ and without hope (Eph 2:12).
God had no basis whatsoever for forgiving us if Christ had not paid for our sins. We certainly did not deserve it.
Since Jesus was nailed to a cross having purchased us with his perfect blood God can forgive us for Christ’s sake.
If we think that Christ’s blood was insufficient for our forgiveness then we may still need to plea with God for forgiveness. Many religious systems today are setup to accomplish just that.
Still captive to sin and guilt, religious people continually confess their sins, say ritualistic prayers, and perform good deeds in attempt to earn forgiveness. This despite the fact that the Bible is clear that Christ already died for sins.
There is no reason to do these things if you have already trusted in Christ’s payment for sin. Trying to earn your own forgiveness makes the cross of Christ of none effect!
Instead stop sinning and thank the Lord that he has already forgiven you for Christ’s sake!