Important: First John needs to be read from John's perspective, not Paul's. Ignore this and you may see what John was NOT saying, but you'll miss most of what he WAS saying.
John wrote this letter to a group of believers who were doubting their own relationship to God. Do you think he spoke so much about having confidence because they felt so confident? Listen:
I have NOT written to you because you do NOT know the truth, but BECAUSE YOU DO KNOW it,1 John 2:21
Hmmm . . . sound like maybe they THOUGHT they didn't know the truth? So, why do we read this letter and come away with MORE reasons to doubt? It doesn't fit. This lack of confidence was being fueled by people among them who did NOT belong to God. These impostors created the illusion of having such a deep relationship with God that it caused the believers to question their own.
These things I have written to you concerning those who are trying to deceive you.1 John 2:26
Too obvious to have fooled them? How often has hindsight revealed your OWN gullibility?
John's letter might throw us off, but it made sense to those he wrote it to. They understood that WE didn't refer to THEM, but to the APOSTLES as that group sent by Jesus to proclaim the message of union with God. He contrasts WE with THEY because there was another group vying for this position of authority - the DECEIVERS. [The fact that ALL believers are ALSO sent by Christ is a reality found in what the APOSTLES had to say; the lies of the DECEIVERS would have us believe that only those who meet up to special criteria are qualified.] My paraphrase is from the perspective of John doing a rewrite for our benefit. I've inserted some related thoughts from John & 1 John to reinforce the letter's train of thought. I've even restructured some of the grammar just to keep our favorite verses from breaking the flow of the whole letter.