There are a few suggestions that are complementary to each other, for why Jesus sent the disciples out in pairs. Firstly, it was common Jewish practice. Secondly, it might be that with the evidence of two witnesses, the truthfulness of their message could be recognized and established (see Deuteronomy 17:6). It could also serve as mutual support.1 And lastly, practically it could mean mutual protection, support in preaching and companionship (see Ecclesiastes 4:9–12).
This practice is also found in other passages in the Gospels (see Luke 10:1, Mark 11:1 and Mark 14:13), as well as in the early church (Acts 12:25, Acts 9:38, Acts 11:30, Acts 13:1–3, 1 Corinthians 9:6) when missionaries were sent out in pairs.2
7 And he called the twelve and began to send them out two by two, and gave them authority over the unclean spirits.