Catena Aurea on Mark 6:6–13: Gregory the Great

Further, the Lord sent the disciples to preach, two and two, because there are two precepts of charity, namely, the love of God, and of our neighbour; and charity cannot be between less than two; by this therefore He implies to us, that he who has not charity towards his neighbour, ought in no way to take upon himself the office of preaching.

There follows: “And He commanded them, that they should take nothing for their journey, save a staff only; no scrip, no bread, no money in their purse: but be shod with sandals; and not put on two coats.”