I won't give a short answer because I like to be clear in reasoning out what I am saying
1 John 1:8
If we say we have no sin, we deceive ourselves, and the truth is not in us.
~
The object of the apostle is to show that it is implied in the very nature of the gospel that we are sinners, and that if, on any pretence, we denied that fact, we utterly deceived ourselves.
Barnes
Notwithstanding believers are cleansed from their sins by the blood of Christ, yet they are not without sin; no man is without sin
Gill
Ὅτι that, may be taken merely as a mark of quotation: "If we say, sin we have not." On the phrase to have sin, see on John 16:22, and compare have fellowship, 1 John 1:3. Sin (ἁμαρτίαν is not to be understood of original sin, or of sin before conversion, but generally. "It is obvious that this ἔχειν ἁμαρτίαν (to have sin), is infinitely diversified, according to the successive measure of the purification and development of the new man. Even the apostle John does not exclude himself from the universal if we say" (Ebrard).
Vincent
(5) There is none but need this benefit, because there is none that is not a sinner.
(e) This fully refutes that perfectness of works of supererogation (doing more than duty requires, the idea that excess good works can form a reserve fund of merit that can be drawn on in favour of sinners) which the papists dream of.
(f) So then, John speaks not thus for modesty's sake, as some say but because it is so indeed.
Geneva
1:8 If we say that we have no sin, we deceive ourselves. To say that we have reached a sinless state in which we no longer need the blood of Christ to cleanse us is a deception. This language is in square opposition to the claims of the Perfectionists of all ages
PNT
The confession of sins is a necessary consequence of "walking in the light" (1Jo 1:7)
that we have no sin-"Have," not "have had," must refer not to the past sinful life while unconverted, but to the present state wherein believers have sin even still. Observe, "sin" is in the singular; "(confess our) sins" (1Jo 1:9) in the plural
JFBBC
The apostle then instructs the believer in the way to the continued pardon of his sin. Here we have, 1. His duty in order thereto: If we confess our sins, v. 9. Penitent confession and acknowledgment of sin are the believer's business, and the means of his deliverance from his guilt. And, 2. His encouragement thereto, and assurance of the happy issue. This is the veracity, righteousness, and clemency of God, to whom he makes such confession: He is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness
Henry
...1:8 If we say we do not bear the guilt of sin, we are deceiving ourselves and the truth is not in us.
Once again v. 8 refers to a claim of the opponents. The phrase translated bear the guilt of sin as used in the Gospel of John (9:41, 15:22, 15:24, 19:11) refers to situations where a wrong action has been committed or a wrong attitude already existed, resulting in a state of sin (i.e., guilt). This is the situation of the secessionist opponents. Such people are deceiving themselves. “Deceit” characterizes these opponents: in 1 John 2:26 they are trying to deceive others (the readers); in 3:7 the author again warns his readers against attempted deceit. The attempt of the opponents to deceive others begins with their self-deceit about being guilty of sins committed....
..1:9 But if we confess our sins, he is faithful and righteous, forgiving us our sins and cleansing us from all unrighteousness.
Does the author of 1 John refer here to an initial confession of sins at conversion (when a person becomes a believer), or to ongoing confession of sins in the life of the believer, or possibly to both at the same time? It seems unlikely that the author is worried about the initial justification of the people to whom he is writing: he regards the members of the community who have “remained” and not “gone out” (1 John 2:19) as genuine believers. Thus the author points out that if Christians confess the sins they are aware of, they may be sure that God will forgive their sins and cleanse them not only from those sins they confess but from all unrighteousness....
Bible. org Comm
Verse 8
[8] If we say that we have no sin, we deceive ourselves, and the truth is not in us.
If we say — Any child of man, before his blood has cleansed us.
We have no sin — To be cleansed from, instead of confessing our sins, 1 John 1:9, the truth is not in us - Neither in our mouth nor in our heart.
Verse 9
[9] If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.
But if with a penitent and believing heart, we confess our sins, he is faithful - Because he had promised this blessing, by the unanimous voice of all his prophets.
Just — Surely then he will punish: no; for this very reason he will pardon. This may seem strange; but upon the evangelical principle of atonement and redemption, it is undoubtedly true; because, when the debt is paid, or the purchase made, it is the part of equity to cancel the bond, and consign over the purchased possession.
Both to forgive us our sins — To take away all the guilt of them.
And to cleanse us from all unrighteousness — To purify our souls from every kind and every degree of it.
Wesley
even Wesley the Perfectionist got it, Skinski.