Bede

And he asked them: How many loaves do you have? They said: Seven. The seven loaves are well placed in the mystery of the New Testament, in which the septiform grace of the Holy Spirit, more fully revealed to all the faithful, is both believed in and given. They are not found to be of barley, like those five loaves, with which five thousand men were fed, lest again, as in the law, the vital food of the soul be hidden by bodily sacraments. For the marrow of barley is tightly covered by a very tenacious husk.

On the Gospel of Mark ↗

Remigius of Rheims

Ignorance was not His reason for asking them, but that from their answering seven, the miracle might be noised abroad, and become more known in proportion to the smallness of the number.

Catena Aurea by Aquinas ↗