28 But those of the circumcision meet thou with this question: Whether is harder, for an aged woman, barren and past age, to bear, or for a virgin in the prime of youth to conceive? Sarah was barren, and though it had ceased to be with her after the manner of women, yet, contrary to nature, she bore a child. If, then, it is against nature for a barren woman to conceive, and also for a virgin, either, therefore, reject both, or accept both. For it is the same God who both wrought the one and appointed the other.
For you will not dare to say that it was possible for God in that former case, and impossible in this latter. And again: how is it natural for a man's hand to be changed in a single hour into a different appearance and restored again? How then was the hand of Moses made white as snow, and at once restored again? But you say that God's will made the change. In that case God's will has the power, and has it then no power in this case? That moreover was a sign concerning the Egyptians only, but this was a sign given to the whole world.
But whether is the more difficult, O you Jews? For a virgin to bear, or for a rod to be quickened into a living creature? You confess that in the case of Moses a perfectly straight rod became like a serpent, and was terrible to him who cast it down, and he who before held the rod fast, fled from it as from a serpent; for a serpent in truth it was: but he fled not because he feared that which he held, but because he dreaded Him that had changed it. A rod had teeth and eyes like a serpent: do then seeing eyes grow out of a rod, and cannot a child be born of a virgin's womb, if God wills?
For I say nothing of the fact that Aaron's rod also produced in a single night what other trees produce in several years. For who knows not that a rod, after losing its bark, will never sprout, not even if it be planted in the midst of rivers? But since God is not dependent on the nature of trees, but is the Creator of their natures, the unfruitful, and dry, and barkless rod budded, and blossomed, and bare almonds. He, then, who for the sake of the typical high-priest gave fruit supernaturally to the rod, would He not for the sake of the true High-Priest grant to the Virgin to bear a child?
Source: Catechetical Lectures (New Advent)