1 John 2:20

And ye have an anointing from the Holy One, and ye know all things.

As Morris said, "This is just another way of saying that all of them had received the gift of the Holy Spirit."[55] that is, the earnest of the Holy Spirit, which is given to all believers in Christ following their repentance and baptism into Christ (Acts 2:38f).

And ye know all things ... The marginal reading here, "you all know," is a better rendition because John did not mean they knew everything, else he would hardly have been writing to them. The thing he referred to here is apparent in other places in the letters of John, namely, that, as regards the basic doctrine of Christianity, called "the word" or "the truth" or "the light," the Christians had been adequately enlightened on all these things before they could become Christians. (Jeremiah 31:31-35). Thus he refuted the boasts of the false teachers that they had any vital new truth that could have benefited anyone. When people hear and obey the gospel of Christ, they have already reached the zenith of all knowledge as it regards the eternal redemption of the soul. There is another view of this passage which accepts it as a reference to one of the charismatic gifts mentioned by Paul in 1 Corinthians 1:8, that is, "the discerning of spirits."[56] The thought behind this is that congregations generally, at the time John wrote, had among their members certain persons endowed with that gift; hence there was no need for them to be led away by false teachers if they heeded the information already available to them from that source. Although the other interpretation is preferred here, this one may not be ruled out altogether as possibly the true one.

[55] Leon Morris, op. cit., p. 1264.

[56] James Macknight, op. cit., p. 54.