7 As weak, then, He nourishes the weak, as a hen her chickens; for He likened Him self to a hen: “How often,” He says to Jerusalem, “would I have gathered your children under my wings, as a hen her chickens; but you would not!” And you see, brethren, how a hen becomes weak with her chickens. No other bird, when it is a mother, is recognized at once to be so. We see all kinds of sparrows building their nests before our eyes; we see swallows, storks, doves, every day building their nests; but we do not know them to be parents, except when we see them on their nests.
But the hen is so enfeebled over her brood, that even if the chickens are not following her, if you see not the young ones, yet you know her at once to be a mother. With her wings drooping, her feathers ruffled, her note hoarse, in all her limbs she becomes so sunken and abject, that, as I have said, even though you see not her young, yet you perceive her to be a mother. In such manner was Jesus weak, wearied with His journey. His journey is the flesh assumed for us. For how can He, who is present everywhere, have a journey, He who is nowhere absent?
Whither does He go, or whence, but that He could not come to us, except He had assumed the form of visible flesh? Therefore, as He deigned to come to us in such manner, that He appeared in the form of a servant by the flesh assumed, that same assumption of flesh is His journey. Thus, “wearied with His journey,” what else is it but wearied in the flesh? Jesus was weak in the flesh: but do not become weak; but in His weakness be strong, because what is “the weakness of God is stronger than men.”
Source: Tractates on the Gospel of John (New Advent)