John 15:6

If a man abide not in me
Christ does not say, "if ye abide not in me"; he would not suppose this of his true disciples; Judas now being removed, to whom he may have some respect in this verse; though it may be applied to anyone who has made a profession of Christ, and denies the truths of the Gospel, neglects the ordinances of it, or walks unworthy of his profession: of whom the following things may be truly said,

he is cast forth as a branch;
that is unfruitful, and is therefore taken away from the vine, and cast forth out of the vineyard. This signifies the ejection of worthless and fruitless professors out of the churches; for such who are either unsound in their principles, or are remiss and negligent in their attendance on the worship of God, with the church, or are loose and vain in their lives and conversations, are to be removed from communion with the people of God.

And is withered.
Some versions, as the Arabic, Syriac, and Persic, read this as an epithet of the word "branch", thus; "the branch that is withered"; expressing the condition the branch is in before it is cast forth out of the vineyard, and the reason of its being cast forth: but others read it as a new and distinct predicate of the branch, showing the case it is in, immediately upon its being cast forth: it may be cut off, and cast out with its leaves upon it, though without fruit; but as soon as ever it is ejected, it withers away. So mere external professors of religion, when they are cast out, of the communion of the church, presently the leaf of profession, which once seemed green, decays, loses its verdure, and that seeming fruit which grew upon them shrinks to nothing, and they become "trees whose fruit withereth, without fruit", ( Jude 1:12 ) : their show of life, zeal, religion, and holiness, disappears, and all their external gifts, light, knowledge, and understanding, even in a speculative way, vanish:

and men gather them;
or, as some copies have it, (auto) , "it", which best agrees with the word "branch". This was a common thing, when branches were thrown out of a vineyard, for men to come and gather them up for an use hereafter mentioned. So when unworthy members are put out of a church of Christ, the men of the world gather them into their society: or they are taken into the congregations of false teachers, who being sensual, and without the Spirit, separate themselves; or it may be read impersonally, "they are gathered", or "it is gathered": so wicked men, and Christless professors, will be gathered by the angels at the last day, and severed by them from the righteous, whom they will place at Christ's left hand to receive their awful doom:

and cast them,
or "it",

into the fire, and they are burned,
or "it is burned"; for nothing else is such a branch good for; see ( Ezekiel 15:2-5 ) . This may respect either the gnawings of conscience, that distress of mind, if not despair, that fearful looking for of judgment, and fiery indignation, which attend apostates in this life; or their being cast into the everlasting burnings of hell fire by angels at the last day, as will be the case of every unfruitful tree, of the chaff and tares.