Why bother is it is hypothetical?
John presents a hypothetical statement found in verses 6, 8, 10 that demand negative consequences.
John presents hypothetical statements found in the verses of 7 and 9 that demand positive consequences.
The hypothetical nature is that he is neither asserting or denying these things are realities in regard to "we" but simply presenting necessary negative and postive conclusions if they are true.
For example, take verse 6. IF we say we have fellowship with him but in addition to that claim we walk in darkness (the hypothetical assertion) then the necessary NEGATIVE conclusion in regard to "we" is "we lie, and do not the truth.
For example, take verse 7. In contrast ["but"]to that NEGATIVE hypothetical consideration in verse 6 IF the following is true - "we walk in the light" then the necessary postive conclusion is also true - "we have fellowship one with another, and the blood of Christ cleanses us from all sin"
This is the hypothetical pattern he follows in verses 6-10. Verse 6 sets forth the hypothetical contrast followed by a negative conclusion while verse 7 responds in a postive contrast and postive conclusion.
Verse 8 sets forth the hypothetical negative followed by a necessary negative conclusion while verse 9 responds sets forth a postive hypothetical assertion followed by a necessary postive conclusion.
Verse 10 sets forth a hypothetic negative assertion followed by a necessary negative conclusion.
6 (A) If we say that we have fellowship with him,
and walk in darkness(B) we lie, and do not the truth:
7 (A) But if we walk in the light, as he is in the light,
(B) we have fellowship one with another, and the blood of Jesus Christ his Son cleanseth us from all sin.
8 ¶ (A) If we say that we have no sin,
(B) we deceive ourselves, and the truth is not in us.
9 (A) If we confess our sins,
(B) he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.
10 (A) If we say that we have not sinned,
(B) we make him a liar, and his word is not in us.