Jesus linked repentance with salvation (Matthew 4:17; Luke 13:3; 17:3).

In Acts 2:38, the term repentance includes the element of faith. Paul in Ephesus preached turning “to God in repentance” and “faith in our Lord Jesus Christ” (Acts 20:21). Repentance is an ingredient of faith. It is a change of mind that involves both a negative aspect (a turning from sin) and a positive one (a turning to God). On Mars Hill, Paul declared that God “commands all people everywhere to repent, because He has fixed a day on which He will judge the world in righteousness by a Man whom He has appointed; and of this He has given assurance to all men by raising Him from the dead” (Acts 17:30-31 ESV).

Even the most mature Christian harbors unconscious sin (Proverbs 20:9; Isaiah 53:6; 1 John 1:8) and will be corrected by the Holy Spirit as hidden sin is brought to the surface. When Christians come to the realization that they have been committing serious sins, there are two reasons they should repent. The first is to express the genuineness of their faith. (A person who is unwilling to renounce continuing, conscious, serious sin may not be a genuine believer.) The second reason is to maintain a close relationship with their Father in heaven.

As Judge, God declared us pardoned and accepted into His family when we put our trust in Jesus. But as God’s children, we can remain in close fellowship to Him only when we daily acknowledge our sins and ask His help in overcoming them. Jesus said that a person who has been bathed doesn’t need another bath; his only need is to have his feet washed.

Jesus . . . rose from supper and laid aside His garments, took a towel and girded Himself. After that, He poured water into a basin and began to wash the disciples’ feet, and to wipe them with the towel with which He was girded. Then He came to Simon Peter. And Peter said to Him, “Lord, are You washing my feet?” Jesus answered and said to him, “What I am doing you do not understand now, but you will know after this.” Peter said to Him, “You shall never wash my feet!” Jesus answered him, “If I do not wash you, you have no part with Me.” Simon Peter said to Him, “Lord, not my feet only, but also my hands and my head!” Jesus said to him, “He who is bathed needs only to wash his feet, but is completely clean; and you are clean, but not all of you.” For He knew who would betray Him; therefore He said, “You are not all clean” (John 13:3-11 NKJV).

The bath of which Jesus spoke is that once-for-all, complete cleansing received at salvation. Foot washing symbolizes the family forgiveness maintained by daily repentance and confession.

First John 1:9 declares, “If we confess our sins, He is faithful and just to forgive us our sins and to cleanse us from all unrighteousness” (NKJV). By practicing the words of this verse, we enjoy our relationship with our heavenly Father and we grow in likeness to Him. The daily cleansing we receive through repentance and confession will also make us less vulnerable to temptation and readier to do His will.
https://questions.org/attq/if-a-christian-believer-is-already-saved-why-is-ongoing-repentance-necessary/