John writes so that the readers may have fellowship with the apostolic witnesses and with the Father and his Son. The message is that God is light; walking in the light brings fellowship and cleansing. These are the end times — the final hour — and many antichrists have already arisen. The call is to remain in what was heard from the beginning.
The darkness is passing away and the true light already shines. The world is passing away with its lusts, but the one who does the will of God remains forever.