A person's sins are forgiven completely past, present and future by Jesus when they are born again. This puts them in a permanent relationship with Jesus.
John 3:16, John 5:24, John 10:28, Ephesians 2:8-9
This is justification.
Now, a born again believer can then either pursue Jesus, or not. If they choose to pursue.. they build a CLOSER relationship with Jesus. They experience an abundant life in Jesus.
If they do not pursue.. get caught up in the world, they are then disciplined, rebuked. But -- Jesus had justified them already. That remains.
Like a relationship a child has in a family.. they are born into the family.. that is permanent.. doesn't change. But they can then either learn from and love their parents or not. That will determine how close they are in intimacy with their parents.
So, what you have is two facets. The unconditional part.. at the point of being born again into God's Family. Then the conditional part.. which does not affect the unconditional part.. and that is closeness that a believer builds with Jesus.
Sins are forgiven.. but they will still affect the rewards 'the crown' that a believer gets when they die and be with Jesus. Everybody sins.. but we do have the ability to 'build treasures in heaven'.
(1Co 3:11) For other foundation can no man lay than that is laid, which is Jesus Christ.
(1Co 3:12) Now if any man build upon this foundation gold, silver, precious stones, wood, hay, stubble;
(1Co 3:13) Every man's work shall be made manifest: for the day shall declare it, because it shall be revealed by fire; and the fire shall try every man's work of what sort it is.
(1Co 3:14) If any man's work abide which he hath built thereupon, he shall receive a reward.
(1Co 3:15) If any man's work shall be burned, he shall suffer loss: but he himself shall be saved; yet so as by fire.
The foundation is never removed by Jesus. But the foundation can be built on by living in closeness to Jesus.