Either allow the tree to be good, and it's fruit good; or shew the tree to be corrupt, and it's fruit corrupt: for the tree is known by it's fruit.

so every good tree yieldeth good fruit, but a corrupt tree produces bad fruit:

a good tree cannot produce evil fruit, nor can a corrupt tree bear good fruit:

and seeing a fig-tree by the way, He went up to it, and finding nothing upon it but leaves, He saith to it, Let no fruit ever hereafter grow out of thee: and the fig-tree withered immediately.

And now the ax is laid to the root of the trees; every tree therefore, which yieldeth not good fruit, is cut down and cast into the fire.

and every tree that bringeth not forth good fruit is cut down and cast into the fire.