For - Ὅτι Hoti. This word “for” is not here to be regarded as connected with the previous verse, and as giving a reason why there should be the exercise of mutual love, but is rather to be understood as connected with the following verse, 2 John 1:8, and as giving a reason for the caution there expressed: “Because it is a truth that many deceivers have appeared, or since it has occurred that many such are abroad, look to yourselves lest you be betrayed and ruined.” The fact that there were many such deceivers was a good reason for being constantly on their guard, lest they should be so far drawn away as not to receive a full reward.
Many deceivers are entered into the world - Are abroad in the world, or have appeared among men. Several manuscripts read here, “have gone out into the world,” (ἐξῆλθον exēlthon,) instead of “have entered into,” εἰσῆλθον eisēlthon. The common reading is the correct one, and the other was originated, probably, from the unusual form of the expression, “have come into the world,” as if they had come from another abode. That, however, is not necessarily implied, the language being such as would he properly used to denote the idea that there were such deceivers in the world.
Who confess not that Jesus Christ is come in the flesh - Who maintain that he assumed only the appearance of a man, and was not really incarnate. See the notes at 1 John 4:2-3.
This is a deceiver - Everyone who maintains this is to be regarded as a deceiver.
And an antichrist - See the notes at 1 John 2:18; 1 John 4:3.