He Explains the Fruits of the Earth (Ver. 29) of Works of Mercy
38 I would also say, O Lord my God, what the following Scripture reminds me of; yea, I will say it without fear. For I will speak the truth, Thou inspiring me as to what You will that I should say out of these words. For by none other than Your inspiration do I believe that I can speak the truth, since You are the Truth, but every man a liar. And therefore he that “speaks a lie, he speaks of his own;” therefore that I may speak the truth, I will speak of Yours. Behold, You have given unto us for food “every herb bearing seed,” which is upon the face of all the earth, “and every tree in the which is the fruit of a tree yielding seed.” Nor to us only, but to all the fowls of the air, and to the beasts of the earth, and to all creeping things; but unto the fishes, and great whales, You have not given these things.
Now we were saying, that by these fruits of the earth works of mercy were signified and figured in an allegory, the which are provided for the necessities of this life out of the fruitful earth. Such an earth was the godly Onesiphorus, unto whose house You gave mercy, because he frequently refreshed Your Paul, and was not ashamed of his chain. This did also the brethren, and such fruit did they bear, who out of Macedonia supplied what was wanting unto him. But how does he grieve for certain trees, which did not afford him the fruit due unto him, when he says, “At my first answer no man stood with me, but all men forsook me: I pray God that it may not be laid to their charge.” For these fruits are due to those who minister spiritual doctrine, through their understanding of the divine mysteries; and they are due to them as men.
They are due to them, too, as to the living soul, supplying itself as an example in all continency; and due unto them likewise as flying creatures, for their blessings which are multiplied upon the earth, since their sound went out into all lands.
Source: Confessions (New Advent)