1 Jn 1:9 teaches conditional forgiveness (if/then) and so contradicts Col 2:13 and Rom 8:1.
You can NOT believe, practice and stand upon 1 John without contradicting Paul on several points, and vice versa. It is impossible.
The only way to harmonize them is to keep them exactly where they already are: separate. Two different audiences, two different commissions, two different contexts, two different dispensations. Keep that in mind and the contradiction vanishes. Seek to practice both and you twist the Word of God unto your own destruction.
You could read I John 1:9 that way.
However, it need not be that way.
I John 1:9
If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.
I John 1:9 is in the context of fellowship with God, with His son and with fellow believers, walking in light, not salvation.
I John 1:3-10
That which we have seen and heard
declare we unto you, that ye also may have fellowship with us: and truly our fellowship is with the Father, and with his Son Jesus Christ.
4 And these things write we unto you, that your joy may be full.
5 This then is the message which we have heard of him, and declare unto you,
that God is light, and in him is no darkness at all.
6 If we say that we have fellowship with him, and walk in darkness, we lie, and do not the truth:
7 But
if we walk in the light, as he is in the light, we have fellowship one with another, and the blood of Jesus Christ his Son cleanseth us from all sin.
8
If we say that we have no sin, we deceive ourselves, and the truth is not in us.
9 If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.
10
If we say that we have not sinned, we make him a liar, and his word is not in us.
Do you ever apologize for wrong doing to your family or friends or co workers or fellow believers or wrongdoing to God?
Why would you since you are righteous?
Maybe because you actually did wrong and you are trying to heal the wounds you caused?
Maybe because apologizing indicates to the ones you wronged that you acknowledged you wronged them?
or would you rather just tell them you did no wrong and that you are righteous?
God's word tells us how to have healthy, growing relationships with those we love.
That includes doing right, that is claiming our righteousness, but it also includes admitting our error to the end of correcting our behavior.
Unless, of course, you wish to suggest that you have no sin.
It deals with post resurrection, post ascension, post Pentecost issues. I John 3:1-3 It speaks of the return of Christ and how that should motivate us to purify ourselves, to do right, after all we are claiming our righteousness, we should be living rightly.
Why does God have us know what is in I John ?
I John 2:1 That we sin not.
My little children, these things write I unto you,
that ye sin not. And if any man sin, we have an advocate with the Father, Jesus Christ the righteous:
If we claim his righteousness we are doing a righteous act.
Since we claim righteousness we should be living accordingly.
Living accordingly means keeping His word, thus the love of God is perfected in us and we know we are in Him, that is in fellowship with God.
I John 2:5
But whoso keepeth his word, in him verily is the love of God perfected: hereby know we that we are in him.