Origen
Catena Aurea · Lukasevangelium 10
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.
Likewise also the twelve were reckoned by two and two, as Matthew shews in his enumeration of them. (Matt. 10:2.) For that two should be joined in service, seems from the word of God to be an ancient custom. For God led Israel out of Egypt by the hands of Moses and Aaron. Joshua and Caleb also, united together, appeased the people who had been provoked by the twelve spies. (Numb. 13, 14. Ex. 12.) Hence it is said, A brother assisted by a brother is as a fortified city. (Prov. 18:19. Vulg.)