"Pray, then, in this way: . . . And forgive us our debts, as we also have forgiven our debtors. . . ." Matthew 6:9-13
"When you pray, say: . . . And forgive us our sins, For we ourselves also forgive everyone who is indebted to us. . . ." Luke 11:2-4
If Christians are already forgiven—past, present, and future—why are we required to daily ask God for forgiveness? Some professing Christians actually have the audacity and nerve to argue that asking God for forgiveness is unnecessary.
"If we confess our sins, He is faithful and righteous to forgive us our sins and to cleanse us from all unrighteousness. If we say that we have not sinned, we make Him a liar and His word is not in us." 1 John 1:9-10
There is a difference between positional and practical. If more Christians actually demonstrated their professed love for God by reading His Word, they would know the Bible better and understand this. Why are we to confess our sins? Let us find out from "a man after [God's] own heart" (1 Sam. 13:14). God disciplined David, a regenerate man of faith, because of his failure to confess his sin. Observe how tormented David was until he confessed his sin and obtained God's forgiveness.
When I kept silent about my sin, my body wasted away
Through my groaning all day long.
For day and night Your hand was heavy upon me;
For day and night Your hand was heavy upon me;
My vitality was drained away as with the fever heat of summer.
I acknowledged my sin to You,
And my iniquity I did not hide; I said,
"I will confess my transgressions to the LORD";
And You forgave the guilt of my sin.
Psalm 32:3-5
Having to ask for God's forgiveness daily for the sins we commit on a daily basis does not mean that we need to "get saved" all over again every time that we sin. Jesus said that, "He who has bathed needs only to wash his feet, but is completely clean" (John 13:10). While we have been fully justified, we have not been fully sanctified. Even though the sins we commit as regenerate believers do not in any way nullify our salvation, nevertheless they do fracture our relationship with God. We continue to confess our sin and seek God's forgiveness in order to maintain a clear conscience and a right standing before God and to preserve our fellowship with Him.
"For by one offering He has perfected for all time those who are sanctified." Hebrews 10:14