For I rejoiced greatly, when the brethren came and testified of the truth that is in thee, even as thou walkest in the truth.

People's New Testament

1:3 For I rejoiced greatly. Certain brethren had been where Gaius lived, had enjoyed his hospitality and had spoken well of him to John on their return.

Wesley's Notes

1:3 For - I know thou usest all thy talents to his glory. The truth that is in thee - The true faith and love.

Jamieson-Fausset-Brown Bible Commentary

3. testified of the truth that is in thee-Greek, "of" (or 'to') thy truth": thy share of that truth in which thou walkest [Alford].

even as thou-in contrast to Diotrephes (3Jo 9).

Matthew Henry's Concise Commentary

1:1-8 Those who are beloved of Christ, will love the brethren for his sake. Soul prosperity is the greatest blessing on this side heaven. Grace and health are rich companions. Grace will employ health. A rich soul may be lodged in a weak body; and grace must then be exercised in submitting to such a dispensation. But we may wish and pray that those who have prosperous souls, may have healthful bodies; that their grace may shine where there is still more room for activity. How many professors there are, about whom the apostle's words must be reversed, and we must earnestly wish and pray that their souls might prosper, as their health and circumstances do! True faith will work by love. A good report is due from those who receive good; they could not but testify to the church, what they found and felt. Good men will rejoice in the soul prosperity of others; and they are glad to hear of the grace and goodness of others. And as it is a joy to good parents, it will be a joy to good ministers, to see their people adorn their profession. Gaius overlooked petty differences among serious Christians, and freely helped all who bore the image, and did the work of Christ. He was upright in what he did, as a faithful servant. Faithful souls can hear their own praises without being puffed up; the commendation of what is good in them, lays them at the foot of the cross of Christ. Christians should consider not only what they must do, but what they may do; and should do even the common actions of life, and of good-will, after a godly sort, serving God therein, and designing his glory. Those who freely make known Christ's gospel, should be helped by others to whom God gives the means. Those who cannot themselves proclaim it, may yet receive, help, and countenance those who do so.