If we say that we have fellowship with Him and yet walk in the darkness, we lie and do not practice the truth; but if we walk in the Light as He Himself is in the Light, we have fellowship with one another, and the blood of Jesus His Son cleanses us from all sin. If we say that we have no sin, we are deceiving ourselves and the truth is not in us. If we confess our sins, He is faithful and righteous to forgive us our sins and to cleanse us from all unrighteousness. I John 1:6-9 NASB
There are several "ifs" in these few verses, all regarding the thinking and behavior patterns of born-again believers. These particular "ifs" in the koine greek language mean "if and it may or may not be true of the individual believer's practice." That's the way we English speakers always interpret "if," but it has different connotations in the greek construct, depending on grammatical class and condition. I am stressing this point to be clear: a person can be a born-again Christian and yet walk in darkness (carnality, ignorance of the Word, dominated by one's old sin nature). Believers in this condition are experts at kidding themselves into believing they are rocking along OK ("me and Jesus, we got our own thing going", ad nauseum.) Such a one, claiming to be in fellowship (koinonia, sharing of common interests) with God the Father, is simply lying to himself and others. Your child doesn't cease to be your child because he is a rebellious brat, but the brat doesn't share your norms and standards.
To have fellowship with the Father, we must walk in the light (spirituality, knowledge of the Word.) You cannot love and practice what you don't know. You cannot advocate what you don't honor. Walking in the light, we know we share the priorities of our Lord, and we know the blood (spiritual death on the cross) of Jesus CONTINUES TO CLEANSE US, KEEPS ON CLEANSING US from all sin. That's what it means. To deny the fact of the old sin nature in our bodies is self-deceit. That corruption is with us as long as we remain in these bodies. But here's the solution: when we see that we have sinned, we confess (admit) that sin (name it to God the Father, in private). He is faithful to always do the same thing, because of Jesus' atonement: He forgives that sin, and He cleanses us from all the other sins we are too immature to recognize as sin in ourselves ("all unrighteousness") because Jesus paid the full penalty for all these sins on the cross. This renews our fellowship with Him, fills our being with the Holy Spirit, and enables us to grow in grace and knowledge of our Lord Jesus Christ. Next time, we'll have a better understanding of just what constitutes sin. We learn to see sin and spirituality as God sees them. We learn to love being in fellowship (agreement) with Him.
This makes us clean and free! The Holy Spirit can now instantaneously fill us, give us understanding, and we are qualified to serve our Lord. We sheep are totally dependent on our Shepherd, both for our eternal salvation and for our daily cleansing. It is His Work! Refusing to submit to this grooming by the Shepherd leaves us in a state of filth and uselessness (sheep cannot clean themselves), unfit for service in His Kingdom and under constant discipline from our Father.
The instruction is not to wallow in sorrow for the sin you have recognized. The instruction is to admit the sin to God and be cleansed.
Be clean. Be free. Be able to learn, to grow, and to serve.