I John 2:15-21
In a Nutshell
John explains the life-focus for followers of Jesus the Messiah, the Son of God.
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God so loved the world. Why then are those who believe in the only begotten Son of God instructed that they must not love the world?
You must not love the world or anything in the world. When anyone loves the world this person is a stranger to the love of the Father; 16 for all that resides in the world - the desires of the flesh, the desires of the eyes, and pride in one's possessions - comes not from the Father but from the world. 17 And the world and the desires bound up with it are on the way out, but the one carrying out the will of God lives on henceforth. 18 Children, we are in the last hour! You will have heard that the antichrist is due, so now many antichrists have turned up. This confirms for us that we know the last hour has come. 19 They went out from us, but they did not belong to us; had they belonged to us, they would have remained with us. But by going out they made it plain that they were not completely with us. 20 But since yours is an anointing by the Holy One your knowledge is [indeed] complete. 21 I did not write to you because you do not know the truth, but [I wrote] because you do indeed know it and [also] that truth never gives birth to a lie. 22 Who is the liar but the one who denies that Jesus is the Christ? This is the antichrist, the one who denies the Father and the Son. 23 No one who denies the Son has the Father; everyone who confesses the Son has the Father also.
The love [AGAPATE] to be shown by the belovéd [AGAPETOI - 2:7], the adopted family of the Father in the Son of God, is truly "in Him and in you" [2:8]. It is not given to be transferred to the world or anything in the world. That means that the given conditions of our life under heaven are not to replace - indeed cannot replace - the love given to us by our Heavenly Father.
John notes that it is possible for the love the Father gives [AGAPE] to be misdirected away from His family's life. To misdirect that love is to completely by-pass the love of the Father; it is also to radically misunderstand and misappropriate the gifts He showers upon us. When that happens the person or persons involved remain outside His Fatherly embrace even though they have been invited to share in His love.
Such misdirection is to bind oneself to what is on the way out; the world, the desires of the flesh and the desires of the eyes and the vaunting of ego that builds itself up, by living by loving the world and the things of the world. John points out that some who were formerly associated with God's Son have left them; because they have left "us", John says, it is clear that they never truly were with "us", although they were in some way associated with "us".
This also serves to remind us of the passage in the gospels (Mark 9:38-41; Luke 9:49-50), where Jesus corrected John's concern about a man casting out evil spirits in His name who was not following along with them up to Jerusalem.
From this passage in his letter we should certainly not think that John has returned to a previous disposition as if now to require all disciples to drop what they are doing and join the same commune if they are to be numbered in Christ's church. Rather, John is referring to some who had been identified as Jesus' disciples at one time who have since departed from the teaching (i.e. what had been given to the apostles by Jesus Himself) and now have taken another path along which they seek to make Him party to their cause. In the earlier instance Jesus pointed out to John that a disciples should not be so oriented to group membership that he or she fails to see the good things that God allows people to do, good things that can indeed be of great spiritual benefit to Jesus' disciples.
But to forsake this (apostolic) teaching about Jesus is no minor mistake. That, says John, is to completely misunderstand - in fact he goes on to explain this is to believe a lie, and even to make Him out to be a liar, to deny that Jesus is the Christ. John reiterates what he has documented of the teaching of Jesus in his gospel.
… no one can come to me unless it be granted by the Father (6:65).
I am the light of the world; he who follows me will never walk in darkness, but will have the light of life (8:12).
If I am not doing the works of my Father, then do not believe me. But if I do them, even though you do not believe me, believe the works, so that you may know and grasp that the Father is in me and I am in the Father (10:37-38).
And much more besides.