Rembrandt's final word is given in his monumental painting of the Return of the Prodigal Son. Here he interprets the Christian idea of mercy with an extraordinary solemnity, as though this were his spiritual testament to the world.

Unforgettable is the image of the repentant sinner leaning against his father's breast and the old father bending over his son. The father's features tell of a goodness sublime and august; so do his outstretched hands, not free from the stiffness of old age. The whole represents a symbol of all homecoming, of the darkness of human existence illuminated by tenderness, of weary and sinful mankind taking refuge in the shelter of God's mercy.
Source: https://www.wga.hu/frames-e.html?/html/r/rembran/painting/biblic3/prodig2.html

“Receive the Holy Spirit. If you forgive the sins of any, they are forgiven; if you retain the sins of any, they are retained.”  
John 20:21-23

1446 Christ instituted the sacrament of Penance for all sinful members of his Church: above all for those who, since Baptism, have fallen into grave sin, and have thus lost their baptismal grace and wounded ecclesial communion. It is to them that the sacrament of Penance offers a new possibility to convert and to recover the grace of justification. The Fathers of the Church present this sacrament as "the second plank [of salvation] after the shipwreck which is the loss of grace."

980 It is through the sacrament of Penance that the baptized can be reconciled with God and with the Church: 

Penance has rightly been called by the holy Fathers "a laborious kind of baptism." This sacrament of Penance is necessary for salvation for those who have fallen after Baptism, just as Baptism is necessary for salvation for those who have not yet been reborn.

It is not easy to entrust oneself to God's mercy, because it is an abyss beyond our comprehension. But we must! ... "Oh, I am a great sinner!" "All the better! Go to Jesus: He likes you to tell him these things!" He forgets, He has a very special capacity for forgetting. He forgets, He kisses you, He embraces you and He simply says to you: "Neither do I condemn you; go, and sin no more" (Jn 8:11).  -- Pope Francis

“All grace flows from mercy, and the last hour abounds with mercy for us.  Let no one doubt concerning the goodness of God; even if a person’s sins were as dark as night, God’s mercy is stronger than our misery.  One thing alone is necessary; that the sinner set ajar the door of his heart, be it ever so little, to let in a ray of God’s merciful grace, and then God will do the rest.”
 
-- Our Lord to Saint Faustina