The story of the Prodigal Son is literally about how God deals with us when we sin and what sin does to us. In the story, the PS renounced his father, took his inheritance and left. In Jewish tradition, that son would be dead to his father, i.e. he would not be accepted back. But in this case the father welcomed the son with open arms when the son came back expressing his contrition, even though it was an imperfect contrition.
This shows several things. That mortal sin makes us dead to God. That confessing our sins restores our relationship with God. And, no matter what we do, God is always more than happy to welcome us back and will even celebrate our reconciliation.
