[LXXII. Ben.]
On the words of the Gospel, Matthew 12:33 , “Either make the tree good, and its fruit good,” etc.
1. The Lord Jesus has admonished us, that we be good trees, and that so we may be able to bear good fruits. For He says, “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.” When He says, “Make the tree good, and his fruit good;” this of course is not an admonition, but a wholesome precept, to which obedience is necessary. But when He says, “Make the tree corrupt, and his fruit corrupt;” this is not a precept that you should do it; but an admonition, that you should beware of it. For He spoke against those, who thought that although they were evil, they could speak good things or have good works. This the Lord Jesus says is impossible. For the man himself must first be changed, in order that his works may be changed. For if a man abide in his evil state, he cannot have good works; if he abide in his good state, he cannot have evil works.
Source: Sermons on Selected Lessons of the New Testament (New Advent)