6 Wherefore nothing is without meaning; everything is significant, but requires one that understands: for even this number of the people fed, signified the people that were under the law. For why were there five thousand, but because they were under the law, which is unfolded in the five books of Moses? Why were the sick laid at those five porches, but not healed? He, however, there cured the impotent man, who here fed multitudes with five loaves. Moreover, they sat down upon the grass; therefore understood carnally, and rested in the carnal.
“For all flesh is grass.” And what were those fragments, but things which the people were not able to eat? We understand them to be certain matters of more hidden meaning, which the multitude are not able to take in. What remains then, but that those matters of more hidden meaning, which the multitude cannot take in, be entrusted to men who are fit to teach others also, just as were the apostles? Why were twelve baskets filled? This was done both marvellously, because a great thing was done; and it was done profitably, because a spiritual thing was done.
They who at the time saw it, marvelled; but we, hearing of it, do not marvel. For it was done that they might see it, but it was written that we might hear it. What the eyes were able to do in their case, that faith does in our case. We perceive, namely, with the mind, what we could not with the eyes: and we are preferred before them, because of us it is said, “Blessed are they who see not, and yet believe.” And I add that, perhaps, we have understood what that crowd did not understand. And we have been fed in reality, in that we have been able to get at the pith of the barley.
Source: Tractates on the Gospel of John (New Advent)