Matthew 3:1
Now in those days Luke 3:1. And in the fifteenth year It could not be gathered from Matthew and Mark in what year of his age John began to preach: but Luke shows sufficiently, that he was about thirty years of age. The ancient writers of the Church are almost unanimously agreed, that he was born fifteen years before the death of Augustus. His successor Tiberius had held the government of the Roman Empire for fifteen years, when the same John began to preach. In this way are made up the thirty years which I have mentioned. Hence it follows, that he did not long discharge the office of teacher, but, in a short time, gave way to Christ; for we shall soon find, that Christ also was baptized in the thirtieth year of his age, when he was immediately installed into the discharge of his public office. Now as John, the morning-star, or dawn, was immediately followed by Christ, “the Sun of Righteousness,” (Malachi 4:2,) there is no reason to wonder, that John disappeared, in order that Christ might shine alone in greater brightness.