Gregory the Great
Catena Aurea · Lukasevangelium 10
Lk 10, Verses 1–2English original
After these things the Lord appointed other seventy also, and sent them two and two before his face into every city and place, whither he himself would come. Therefore said he unto them, The harvest truly is great, but the labourers are few: pray ye therefore the Lord of the harvest, that he would send forth labourers into his harvest. It follows, And he sent them two and two.
(Hom. 17. in Ev.) He sends the disciples to preach two and two, because there are two commands of charity, the love of God, and love of our neighbour; (and charity cannot exist without at leasttwo;) thereby silently suggesting to us, that he who has not love to another, ought not to undertake the office of preaching.