De gratia Christi 18, 19.
Quote 08 30
On the supposition, therefore, that two trees, one good and the other corrupt, represent two human beings, a good one and a bad, what else is the good man except one with a good will, that is, a tree with a good root? And what is the bad man except one with a bad will, that is, a tree with a bad root? The fruits which spring from such roots and trees are deeds, are words, are thoughts, which proceed, when good, from a good will, and when evil, from an evil one.