Albert Barnes Commentary 3 John 1:8

"We therefore ought to welcome such, that we may be fellow-workers for the truth." — 3 John 1:8 (ASV)

We therefore ought to receive such. All of us ought hospitably to entertain and aid such persons. The work in which they are engaged is one of pure benevolence. They have no selfish aims and ends in it. They do not even look for the supplies of their needs among the people to whom they go to minister; and we ought, therefore, to aid them in their work, and to contribute to their support. The apostle doubtless meant to urge this duty particularly on Gaius; but in order to show that he recognized the obligation himself, he uses the term "we," and speaks of it as a duty binding on all Christians.

That we might be fellow-helpers to the truth. All Christians cannot go forth to preach the gospel, but all may contribute something to the support of those who do; and in this case they would have a joint participation in the work of spreading the truth. The same reasoning which was applicable to that case, is also applicable now in regard to the duty of supporting those who go forth to preach the gospel to the destitute.