New International Version
Calling the Twelve to him, he began to send them out two by two and gave them authority over impure spirits.
According to Jewish law, they need at least 2 persons to testify and agree. So if their hearers object, they have the required number of persons present to affirm the truthfulness of a statement.
One witness is not enough to convict anyone accused of any crime or offense they may have committed. A matter must be established by the testimony of two or three witnesses.
Even in your own Law it is written that the testimony of two men is valid.
Furthermore, the two can check on each other and support and encourage each other.
They are mutually accountable to each other and to reduce the number of temptations
The formula works well as Jesus did the same on another occasion in Luke 10:1
After this the Lord appointed seventy-two others and sent them two by two ahead of him to every town and place where he was about to go.