John Calvin Commentary Matthew 3:1

"And in those days cometh John the Baptist, preaching in the wilderness of Judaea, saying," — Matthew 3:1 (ASV)

Now in those days. And in the fifteenth year. It could not be determined from Matthew and Mark at what age John began to preach, but Luke shows sufficiently that he was about thirty years of age.

The ancient writers of the Church almost unanimously agree 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. This accounts for the thirty years I have mentioned.

Therefore, it follows that he did not fulfill the office of teacher for long but, in a short time, gave way to Christ. For we will soon find that Christ also was baptized in his thirtieth year, when he was immediately installed in his public office. Now, as John, the morning-star, or dawn, was immediately followed by Christ, the Sun of Righteousness, (Malachi 4:2), it is no wonder that John disappeared, so that Christ might shine alone in greater brightness.