Matthew only (cf. Matthew 3:10, vide infra). Every tree that bringeth not forth good fruit is hewn down, and cast into the fire. A parenthesis expressing the terrible fate of those the general product (verse 16, note) of whose life is not good.
Christ will warn his followers plainly against listening to them. Observe that the form of the sentence ( πᾶν δένδρον μὴ ποιοῦν καρπόν, κ.τ.λ.) implies that all trees will be cut down unless there is a reason for the contrary; that the normal event (the natural result of universal sin, apart, of course, from Christ's atonement) is that men are condemned and perish.
In Matthew 3:10 this general statement is applied ( οὖν) to a definite time of impending judgment.