Gregory the Great
Catena Aurea · Markusevangelium 6
—And he went round about the villages, teaching. And he called unto him the twelve, and began to send them forth by two and two; and gave them power over unclean spirits; And 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. And he said unto them, In what place soever ye enter into an house, there abide till ye depart from that place. And whosoever shall not receive you, nor hear you, when ye depart thence, shake off the dust under your feet for a testimony against them. Verily I say unto you, It shall be more tolerable for Sodom and Gomorrha in the day of judgment, than for that city. And they went out, and preached that men should repent. And they cast out many devils, and anointed with oil many that were sick, and healed them.
(Hom. in Evan. 17) 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.