I have no greater joy than to hear that my children walk in truth - That they adhere steadfastly to the truth, and that they live in accordance with it. This is such language as would be used by an aged apostle when speaking of those who had been converted by his instrumentality, and who looked up to him as a father; and we may, therefore, infer that Gaius had been converted under the ministry of John, and that he was probably a much younger man than he was. John, the aged apostle, says that he had no higher happiness than to learn, respecting those who regarded him as their spiritual father, that they were steadfast in their adherence to the doctrines of religion. The same thing may be:
(a) of all the ministers of the gospel, that their highest comfort is found in the fact that those to whom they minister, whether still under their care or removed from them, persevere in a steadfast attachment to the true doctrines of religion, and live accordingly; and,
(b) of all Christian parents respecting their own children. the highest joy that a Christian parent can have is to know that his children, whether at home or abroad, adhere to the truths of religion, and live in accordance with the requirements of the gospel of Christ.
If a child wished to confer the highest possible happiness upon his parents when with them, it would be by becoming a decided Christian; if, when abroad, in foreign lands or his own, he wished to convey intelligence to them that would most thrill their hearts with joy, it would be to announce to them that he had given his heart to God. There is no joy in a family like that when children are converted; there is no news that comes from abroad that diffuses so much happiness through the domestic circle as the intelligence that a child is truly converted to the Saviour. There is nothing that would give more peace to the dying pillow of the Christian parent, than to be able to leave the world with the assurance that his children would always walk in truth.

To hear that my children - From this it has been inferred that Caius was one of St. John's converts, and consequently not the Corinthian Caius, who was converted, most probably, by St. Paul. But the apostle might use the term children here as implying those who were immediately under his pastoral care, and, being an old man, he had a right to use such terms in addressing his juniors both in age and grace; and there is much both of propriety and dignity in the appellation coming from such a person.

I have no greater joy than (a) to hear that my children walk in truth.
(a) Than these joys.

I have no greater joy,.... Nothing that causes greater joy. The Vulgate Latin version reads "grace" or "thanks"; and then the sense is, that he had nothing to be more thankful for:
than to hear that my children walk in truth; meaning his spiritual children, those whose conversion he had been the instrument of; and among these it seems Gaius was one.

my children--members of the Church: confirming the view that the "elect lady" is a Church.

I have no greater joy than this - Such is the spirit of every true Christian pastor. To hear that my children walk in the truth - Caius probably was converted by St. Paul. Therefore when St. John speaks of him. with other believers, as his children, it may be considered as the tender style of paternal love, whoever were the instruments of their conversion. And his using this appellation, when writing under the character of the elder, has its peculiar beauty.