Charity to Christians is reckoned fidelity to Christ, being shown to them upon the Christian account, which is intimated to have been done by this pious person, who so kindly treated the brethren, and strangers, i.e. even though they were strangers.
Related Commentaries of 3 John 1:5
3 John 1:5
5 Beloved, thou doest faithfully whatsoever thou doest to the brethren, and to strangers;