‘You are of God, little children, and have overcome them, because greater is he that is in you than he that is in the world. They are of the world, therefore speak they of the world, and the world hears them.'
But he is confident that the true Christians will not be misled by false prophets because as true Christians they have ‘the anointing' (1 John 2:20; 1 John 2:27). The Holy Spirit is within them. And He will lead them into truth. And the Father and the Son also abide within them (1 John 4:13; 1 John 4:16; 1 John 5:12). They are therefore very much ‘of God'. So greater is He (the Triune God) that is in them than the one who is in the world. That is why they overcome ‘them' by not being deceived or led astray, but by holding firmly to the truth and continuing to win men to such truth. The church may sometimes seem to be on the back foot, but it is not. Through Him it goes forward to victory.
On the other hand the place for the false prophets is the world, for they are not ‘of God' they are ‘of the world', and speak what befits the world, and the world listens to them. To the world they are popular. They are ‘of the world' because there is nothing heavenly about their message (although they would probably have been annoyed at such a suggestion). The content and effects of their teaching are strictly limited to this world and its fantasies and are not harsh on sin.
‘He that is in the world' could here simply signify each and any false prophet, seen first singly and then in the plural, which might be suggested by the immediate move from ‘he' to ‘they'. But there may be the thought behind it of the Evil One, who lies behind these false prophets, although we should note that John does not speak of him as being ‘in the world', rather he describes the whole world as ‘lying in him' (1 John 5:19). So if the latter thought is in mind it is not prominent. On the other hand Christians have earlier been described as ‘overcoming the Evil One' (1 John 2:13), so the mention of overcoming here may well have him in mind, active in the background as he so often is.