William Burkitt on 3 John 1:11

Here St. John advises his beloved Gaius, and those with him, not to imitate and follow this evil example of Diotrephes, (who not only refused charity towards the Christian Jews that wanted it, himself, but would not permit the Gentile Christians to receive them or relieve them,) but to follow the example of God, who is good to all; and, accordingly, he that is merciful is born of God, but he that is malicious hath no true knowledge of God, but is a mere stranger to him. Behold here the euology and high commendation which the Spirit of God gives to charitable and good men: He that doeth good is of God, he is allied to heaven, born of God, and his offspring: but the uncharitable evil man is a composition of spite, envy, and malice, born from beneath, and the devil's offspring.