“For this is the message you heard from the beginning: We should love one another.” - 1 John 3:11
John and Peter, of all the disciples had a special relationship with Jesus. Jesus even allowed them time to commune with Elijah and Moses. John writes in a particular style that is also evident in his letters and in Revelations. Earlier, John had written that Jesus was the Word made flesh. That flesh was sacrificed by God, as a gift to those whom God loved, so that God could abide them Because eternal life is close proximity to God. And to perish is to be utterly riven from God.
Here, John is reminding us that the God of the Old Testament is the same as God in the New Testament.