Passage
and ye have known that he was manifested that our sins he may take away, and sin is not in him;
and ye have known that he was manifested that our sins he may take away, and sin is not in him;
1 John 3:3 and every one who is having this hope on him, doth purify himself, even as he is pure.
1 John 3:4 Every one who is doing the sin, the lawlessness also he doth do, and the sin is the lawlessness,
1 John 3:5 and ye have known that he was manifested that our sins he may take away, and sin is not in him;
1 John 3:6 every one who is remaining in him doth not sin; every one who is sinning, hath not seen him, nor known him.
1 John 3:7 Little children, let no one lead you astray; he who is doing the righteousness is righteous, even as he is righteous,
The verse centers on "known", "manifested", "sins", "take", and "away". It is saying that the verse draws attention to "known" and "manifested", so its meaning should be read from those terms before moving to application.
The nearby context moves from verse 4's "Every one who is doing the sin..." into verse 6's "every one who is remaining in him...", so "known" and "manifested" belong inside that flow. In 1 John context, the local focus is Christ, faith, and discipleship.
A plain takeaway is to answer the verse's own emphasis on "known" and "manifested" with trust shaped by these words, not by a vague optimism outside the passage.