God's forgiveness depends upon what we do to deserve it. Sin is breaking a set of rules established by man. Confession means admitting to God we are wrong.
Every man is a sinner.
Repentance is feeling sorry about your sin. We have been forgiven for all our past, present, and future sin because of the death of Christ. If we fail to confess our sins, we can lose our salvation. Once God has forgiven our sins, He will never bring it up again to hold against us. God is the only One who can forgive us our sins.