Observe here, 1. the person rejoicing, St. John, the apostle and minister of Christ Jesus, I rejoiced greatly.
2. The mercy rejoiced in, their walking in the truth.
It was not their speculative knowledge of the truth, and their taking upon them a bare profession of Christianity, that he rejoiced in, but their walking in the truth, and framing their conversation according to the commandment which they had received from the Father.
Christianity is not a speculative science, but a practical art of holy living; and the most exalted knowledge is insuffucient to salvation, without a suitable and correspondent practice; therefore, says St. John here, I rejoiced greatly to find of thy children, not barely professing of the truth, but walking in the truth.
Observe, 3. The persons rejoiced for, or in the behalf of; the youth in that church or family to which he now wrote, I rejoiced to find thy children walking in the truth; the hopes which the holy apostle had of a succession of saints, and that the children in his time would walk in their religious parents footsteps, was matter of singular joy and rejoicing to the blessed apostle.
Yet observe, 4. With what caution, restriction, and limitation, our apostle speaks, I rejoiced greatly to find of thy children; that is, some of them, perhaps many of them, it is to be feared not all of them; to have seen all was no doubt the apostle's desire, but to find any was questionless matter of exceeding joy: I rejoiced greatly to find of thy children walking in the truth.
Learn hence, That there is no greater joy to the ministers of Christ, than to see the youth, or rising generation, in their day, walking in the paths of holiness and religion, and treading in their religious parents' footsteps.