John Calvin Commentary John 15:6

"If a man abide not in me, he is cast forth as a branch, and is withered; and they gather them, and cast them into the fire, and they are burned." — John 15:6 (ASV)

If any one abide not in me. He again sets before them the punishment for ingratitude, and by doing so, encourages and urges them to perseverance. Perseverance is indeed the gift of God, but the exhortation to fear is not unwarranted, for fear that our flesh, through too much indulgence, might uproot us.

He is cast out, and withered, like a branch. Those who are cut off from Christ are said to wither like a dead branch, because, just as the beginning of strength is from Him, so also is its uninterrupted continuance. It is not that any of the elect ever dry up; rather, it is because there are many hypocrites who, in outward appearance, flourish and are green for a time, but who afterwards, when they ought to yield fruit, show the very opposite of what the Lord expects and demands from His people.