6 You have heard an instance of a literal expression, as “that we shall rise again;” of a literal action, as that, according as it is said, “Paul went up to Jerusalem to see Peter.” “The stone which the builders refused,” is a figurative expression; “the anointed stone” which was at Jacob's head, is a figurative action. There is now due to your expectation an example made out of both together, something which is at once a literal fact, and which also signifies something else figured by it.
“We know that Abraham had two sons, the one by a bondmaid, the other by a free-woman;” this was literally a fact, not only a story, but a fact; are you looking for that which was figured in it? “These are the two Testaments.” That then which is spoken figuratively, is a sort of fiction. But since it has some real event represented by it, and the very figure itself has its ground of truth, it escapes all imputation of falsehood. “The sower went out to sow his seed; and as he sowed, some fell by the way side, some fell upon stony places, some fell among thorns, and some fell upon good ground.” Who went out “to sow,” or when went he out, or upon what “thorns,” or “stones” or “way side” or in what field did he sow?
If we receive this as a fictitious story, we understand it in a figurative sense; it is fictitious. For if any sower really went out, and did cast the seed in these different places, as we have heard, it were no fiction, and so no falsehood. But now though it be a fiction, yet it is no falsehood. Why? Because the fiction has some further signification, it deceives you not. It requires only one to understand it, and does not lead any one into error. And thus Christ wishing to convey this lesson to us, sought for fruit, and hereby set forth to us a figurative, and no deceiving fiction; a fiction therefore worthy of praise, not of blame; not one by the examination of which we might run into what was false; but by the diligent investigation of which we might discover what is true.
Source: Sermons on Selected Lessons of the New Testament (New Advent)