Verse 20: But wilt thou know, O vain man, that faith without works is dead?
[Wilt, etc., θέλεις δὲ γνῶναι, ὦ ἄνθρωπε κενέ] But wilt hou know (now the Apostle speaks [Estius], that is to say, Dost thou wish this to be taught to thee also by examples from the Old Testament [Grotius]: that is to say, If thou art desing to know, come and lend thy ear, I shall instruct thee: Compare John 13:12; Romans 13:3 [Piscator]), O vain man (Beza, Piscator, thus the Arabic, etc.), or, feeble (the Syriac in Grotius), that is, with respect to judgment, ריקא/Raca, which word was discussed in Matthew 5:22. Christ prohibits the wrath that rushes forth in such words, not the words themselves, when they are used by teachers to correct their disciples; and much less when not particular men are being thus branded, but certain sorts of men. This appears in Matthew 23:17, 19; Luke 24:25; Galatians 3:1, 3. Vain, that is, who leadest thyself on with vain hope (Grotius), who boastest a vain or empty faith (Piscator, Menochius, Vorstius). He calls the man vain, either because he boasts of what he has not, or because he has not grace’s solidity, stability, or efficacy (Gataker).
But wilt thou know? Either this question is in order to teaching, as John 13:12; Romans 13:3; and then the sense is: If thou hast a mind to know, I shall instruct thee: or, it is a teaching by way of question, as more emphatical and pressing; and then it is as if he had said, Know, O vain man. O vain man; an allusion to an empty vessel, which sounds more than one that is full. The carnal professor to whom he speaks is vain, because empty of true faith and good works, though full of noise and boasting. Objection. Doth not the apostle sin against Christ’s command, Matthew 5:22? Answer: 1. He speaks not of any particular man, but to all in general, of such a sort, viz. who boasted of their faith, and yet did not evidence it by their works. 2. It is not spoken in rash anger, or by way of contempt, but by way of correction and just reproof; see the like spoken by Christ himself, Matthew 23:17, 19; Luke 24:25; and by Paul, Galatians 3:1; 1 Corinthians 15:36.
[Faith without works (that is, idle [Estius]: That χωρὶς ἔργων, without works, depends, either, 1. upon the word πίστις/faith, Faith which is without works, so that there is an Ellipsis of the article ἡ, which sort is found in Matthew 5:21; John 5:36; etc. [Beza]: or, 2. upon those words, νεκρά ἐστιν, is dead [Piscator], with these words understood, ἐὰν ᾖ, if it be [Piscator, thus Grotius], that is, if it have not works: The sense is the same in either case [Piscator]) is dead?] That is, It is without action and motion (Estius): It is not able to produce that for which thou hopest (Grotius): it avails not for the salvation of men (Vorstius).
That faith without works is dead; a defective speech, faith without works, for that faith which is without works, or, faith, if it be without works. He doth not say, faith is dead without works, lest it should be thought that works were the cause of the life of faith; but faith without works is dead, as verses 17, 26; implying, that works are the effects and signs of the life of faith.
 Greek: θέλεις δὲ γνῶναι, ὦ ἄνθρωπε κενέ, ὅτι ἡ πίστις χωρὶς τῶν ἔργων νεκρά ἐστιν;
 That is, ἡ πίστις (with the article ἡ here elided) χωρὶς τῶν ἔργων.
 Matthew 5:21: “Ye have heard that it was said by them of old time, Thou shalt not kill; and whosoever shall kill shall be in danger of the judgment (ὃς δ᾽ ἂν φονεύσῃ, ἔνοχος ἔσται τῇ κρίσει)…”
 John 5:36a: “But I have greater witness than that of John (ἐγὼ δὲ ἔχω τὴν μαρτυρίαν μείζω τοῦ Ἰωάννου)…”