Here the word "you" is plural and refers to the people to whom John wrote as well as all believers. The word "he" is emphatic and refers to Christ. (See: [[rc://en/ta/man/translate/figs-you]])
"remember and believe what you have heard from the beginning." How they heard it, what they heard, and what "the beginning" means can be made explicit: AT: "continue to trust what we have taught you about Jesus just as you have trusted since you first became believers" (See: [[rc://en/ta/man/translate/figs-explicit]])