The family analogy has always helped me in this regard. When I was born, I became a permanent member of the Pritchard family. Being part of that family is my birthright. I could no more become an “un-Pritchard” than I could be “unborn.” I am always a part of my family. The same is true of my three sons. They are always my son. Once a son, always a son.
Could my sons disappoint me? Yes, and I could disappoint my parents when I was growing up.
Could my sons disown me? Yes, that could happen.
Could my sons ever not be my sons? No, that’s impossible. They could change their names but not their true identity.
But inside the family, I could disappoint my parents (and sometimes did). And my boys could disappoint me (and sometimes did). When I hurt my parents by acts of disobedience, I suffered for my foolishness and my “fellowship” was not right until I got right with them. Ditto for me and my boys. Disobedience disrupts family fellowship.
The same is true in the spiritual life. Having been forgiven by the blood of Jesus, I still need daily cleansing for my daily sins. So I ask the Lord to forgive me and restore fellowship between me and him. We see David doing this in Psalm 51. We see the same thing proimsed in 1 John 1:9, “If we confess our sins, he is faithful and just and will forgive us our sins and purify us from all unrighteousness.”