6:7 Why did Jesus send the disciples out two by two?

It was done for legal and practical reasons. In the divine order every word is established in the mouth of two or three witnesses (cp Nu 35:30; Deut 17:6; 19:15; Mt 18:15-16; Jn 8:16-18; 2Cor 13:1; He 10:28 with Ac 13:1-2; 15:27, 32, 37-40; 19:22).

Jesus also sent out other disciples two by two in scripture (cp Mk 14:13; Lk 10:1). Scriptures also teach that two are better than one in many other respects as well.

When one falls the other can lift him up; when one is discouraged the other can encourage him; when one is weak the other can strengthen him; when one is prevailed against the other can stand with him (cp Pr 27:17; Eccl 4:9-12; Ro 15:14).

Two can also prevail with God in unified prayer (cp Mt 18:19-20).

There are many other passages in scripture dealing with the two by two principle (cp Lk 7:19; Jn 1:35-41; Ac 9:38; 10:7; 15:36-41; 19:22; 1Ti 5:19; Rev 11:3-6, 10-12).