{21} But ye have an {p} unction from the {q} Holy One, and ye know all things.

(21) Thirdly, he comforts them, to make them stand fast, as they are anointed by the Holy Spirit with the true knowledge of salvation.

(p) The grace of the Holy Spirit, and this is a borrowed type of speech taken from the anointings used in the law.

(q) From Christ who is peculiarly called Holy.

People's New Testament

2:20 But ye have an unction from the Holy One. Ye are anointed with the Holy Spirit. Christian means an anointed one; Anti-Christ would mean against the Anointed. Hence John reminds them that they have been anointed by the Holy One.

And ye know all things. All things needful to guard against these opposers and seducing teachers. It is the privilege of those who have this anointing to know Christ experimentally (Joh 14:22,23).

Wesley's Notes

2:20 But ye have an anointing - A chrism; perhaps so termed in opposition to the name of antichrist; an inward teaching from the Holy Ghost, whereby ye know all things - Necessary for your preservation from these seducers, and for your eternal salvation. St. John here but just touches upon the Holy Ghost, of whom he speaks more largely, 1Jo 3:24; 4:13; 5:6.

Jamieson-Fausset-Brown Bible Commentary

20. But-Greek, "And." He here states the means which they as believers have wherewith to withstand. Antichrists (1Jo 2:18), namely, the chrism (so the Greek: a play upon similar sounds), or "anointing unguent," namely, the Holy Spirit (more plainly mentioned further on, as in John's style, 1Jo 3:24; 4:13; 5:6), which they ("ye" is emphatical in contrast to those apostates, 1Jo 2:19) have "from the Holy One, Christ" (Joh 1:33; 3:34; 15:26; 16:14): "the righteous" (1Jo 2:1), "pure" (1Jo 3:3), "the Holy One" (Ac 3:14) "of God"; Mr 1:24. Those anointed of God in Christ alone can resist those anointed with the spirit of Satan, Antichrists, who would sever them from the Father and from the Son. Believers have the anointing Spirit from the Father also, as well as from the Son; even as the Son is anointed therewith by the Father. Hence the Spirit is the token that we are in the Father and in the Son; without it a man is none of Christ. The material unguent of costliest ingredients, poured on the head of priests and kings, typified this spiritual unguent, derived from Christ, the Head, to us, His members. We can have no share in Him as Jesus, except we become truly Christians, and so be in Him as Christ, anointed with that unction from the Holy One. The Spirit poured on Christ, the Head, is by Him diffused through all the members. "It appears that we all are the body of Christ, because we all are anointed: and we all in Him are both Christ's and Christ, because in some measure the whole Christ is Head and body."

and-therefore.

ye know all things-needful for acting aright against Antichrist's seductions, and for Christian life and godliness. In the same measure as one hath the Spirit, in that measure (no more and no less) he knows all these things.

Matthew Henry's Concise Commentary

2:18-23 Every man is an antichrist, who denies the Person, or any of the offices of Christ; and in denying the Son, he denies the Father also, and has no part in his favour while he rejects his great salvation. Let this prophecy that seducers would rise in the Christian world, keep us from being seduced. The church knows not well who are its true members, and who are not, but thus true Christians were proved, and rendered more watchful and humble. True Christians are anointed ones; their names expresses this: they are anointed with grace, with gifts and spiritual privileges, by the Holy Spirit of grace. The great and most hurtful lies that the father of lies spreads in the world, usually are falsehoods and errors relating to the person of Christ. The unction from the Holy One, alone can keep us from delusions. While we judge favourably of all who trust in Christ as the Divine Saviour, and obey his word, and seek to live in union with them, let us pity and pray for those who deny the Godhead of Christ, or his atonement, and the new-creating work of the Holy Ghost. Let us protest against such antichristian doctrine, and keep from them as much as we may.