Either make the tree good, and his fruit good; or else make the tree corrupt, and his fruit corrupt: for the tree is known by his fruit. Either make the tree good - That is, the effect will be always similar to the cause; a bad tree will produce bad fruit, and a good tree, good fruit.
The works will resemble the heart: nothing good can proceed from an evil spirit; no good fruit can proceed from a corrupt heart. Before the heart of man can produce any good, it must be renewed and influenced by the Spirit of God.