William Burkitt on 3 John 1:12

Having propounded the example of God in the former verse, he propounds in this the example of Demetrius, as a pattern to them for their imitation in works of piety and charity; not only common report, and the apostle's testimony, but his own good works, did justly recommend him as an extraordinary pattern to their imitation.

Note, That the commendations, which our own good works do give us before the world, are more valuable than all the praises and applauses which can be given to us by men, yea, by the best of men. Demetrius has a good report of all men, yea, of the truth itself.