“Happy is the man whose sin Jehovah will by no means take into account.”
~Romans 4:8

The verse the Apostle Paul is quoting in this passage is a Psalm which continues: “In whose spirit there is no deceit.” (Ps. 32:2)
In order to benefit from the joy of being granted true forgiveness, we must first turn around from our evil course. (Eze. 33:11; Acts 3:19; Ep. 4:22-24)
This implies being humble enough to recognize the error of our ways and a willingness to put in the effort to change.
Once we have demonstrated our repentance, we are able to feel the joy that comes from being reconciled to God through Jesus. (Rom. 5:11)
The knowledge that God loves us and assumes the best in us when we try to please him can carry us joyfully through difficult times. (Rom. 5:2-6)