As I said, the forgiveness of sins can be in regard to fellowship as in this verse written to those who are already saved:
"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 If we say that we have fellowship with him, and walk in darkness, we lie, and do not the truth...If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness" (1 Jn.1:5-6, 9).
The Christians who received this epistle were told that they already possessed eternal life (1 Jn.5:11) and the Lord Jesus said that those to whom He gives eternal life shall never perish:
"And I give unto them eternal life; and they shall never perish, neither shall any man pluck them out of my hand" (Jn.10:28).
So the forgiveness of sins spoken of in chapter 1 cannot be in regard to salvation since they already possessed eternal security.