here is a different take on this passage from Joe Mullen.

A 16.  YE SHALL KNOW THEM 

B BY THEIR FRUITS.

C Do men GATHER grapes of thorns, or figs of thistles?

D 17.  Even so every good tree BRINGETH FORTH GOOD FRUIT;

E but a CORRUPT TREE

F BRINGETH FORTH EVIL FRUIT.

G 18. A good tree

F’ cannot BRING FORTH EVIL FRUIT

E’ neither can a CORRUPT TREE bring forth good fruit.

D’ 19. Every tree that BRINGETH NOT FORTH GOOD FRUIT is hewn down,

C’ and CAST into the fire.

B’ 20. Wherefore BY THEIR FRUITS

A’ YE SHALL KNOW THEM.