13 He who conceals his sins will not prosper;
But he who confesses them and turns aside will obtain mercy.
King James Version
Accepting what God says about sinful behavior and turning away from it is wise because God's free forgiveness will do the rest.
David stated it in the following way:
32 Blessed is he whose transgression has been forgiven, and his sin covered.
2 Blessed is the man whom Jehovah does not blame for iniquity,
And in whose spirit there is no deception.
3 As I fell silent, my bones grew old
In my moaning all day.
4 For day and night your hand was heavy on me;
It became my greenery in summer dryness. Selah
5 I declared my sin to you, and did not cover up my iniquity.
I said: I will confess my transgressions to Jehovah;
And you forgave the evil of my sin. Selah
6 For this, every saint will pray to you in the time when you can be found;
Certainly in the flood of many waters they will not reach him.
7 You are my refuge; You will keep me from anguish;
With songs of deliverance you surround me. Selah
8 I will make you understand, and I will teach you the way in which you must walk;
I will fix my eyes on you.
The joy of forgiveness is indescribable. Expressing it many times is difficult because we certainly cannot find the exact words to describe it and that joy is only given by God through sincere repentance.
The apostle Paul many times used these verses to describe the happiness of the human being whose sins are forgiven by the grace of God, not by his efforts to fulfill the works of the law because really the one who repents and turns away from their sins will receive forgiveness and mercy of God.
In this sense when the psalmist refers to transgression it means rebellion while sin is to miss the mark; iniquity is moral depravity; and also cheating. Sin is forgiven, covered and not imputed to the individual, so that the spirit of the man or the woman appears as totally justified in the eyes of God, reason why David declares that blessed is the one whose transgression has been forgiven.
In this order of ideas, it is not convenient to be complaining all the time and not to act, that is, complaining instead of confessing sins to God, has physical and emotional repercussions. And really when we act and do regret seeking God's forgiveness we are free and we feel joy in our hearts.
When we repent and confess our sins to God he forgives us changes us less transforms us gives us new life and puts peace and joy in our hearts.