John Calvin Commentary Acts 18:25

"This man had been instructed in the way of the Lord; and being fervent in spirit, he spake and taught accurately the things concerning Jesus, knowing only the baptism of John:" — Acts 18:25 (ASV)

He was instructed. What Luke adds shortly after seems not to agree with this commendation, namely, that Apollos knew only the baptism of John. However, this latter point is added by way of correction.

Nevertheless, these two aspects are quite compatible: he understood the doctrine of the gospel, because he knew that the Redeemer had been given to the world and was also well and sincerely instructed concerning the grace of reconciliation. Yet, he had been trained only in the foundational principles of the gospel, to the extent that could be derived from John’s teaching.

For we know that John was midway between Christ and the prophets. His father Zechariah speaks of John's office in his song (Luke 1:76; Luke 1:16–17), as does the angel, drawing from the prophecy of Malachi (Malachi 3:1). Surely, since John carried the light before Christ and highly extolled His power, his disciples are rightly said to have had knowledge of Christ.

Moreover, it is worth noting the phrase that he knew the baptism of John. For from this we gather the true use of the sacraments: namely, that they initiate us into a certain kind of doctrine, or that they establish the faith which we have embraced. Surely, it is wickedness and impious profanation to separate them from doctrine.

Therefore, for the sacraments to be rightly administered, the voice of heavenly doctrine must be heard there. For what is the baptism of John? Luke encompasses all of John's ministry in this phrase, not only because doctrine is joined to baptism, but also because doctrine is its foundation and head, without which baptism would be an empty and dead ceremony.

Being fervent in spirit, he spoke. Apollos receives another commendation in these words: that he was inflamed with a holy zeal to teach. Doctrine without zeal is either like a sword in the hand of a madman, or it lies dormant, cold and useless, or it serves for vain and wicked boasting.

For we see that some learned men become slothful; others (which is worse) become ambitious; still others (which is worst of all) trouble the Church with contention and brawling. Therefore, doctrine not joined with zeal will be unsavory.

But let us remember that Luke puts the knowledge of Scripture in the first place, which must be the moderator of zeal. For we know that many are fervent without consideration, as the Jews raged against the gospel because of a perverse devotion they had for the law. And even today we see what the Papists are, who are carried headlong with furious violence, spurred on by an opinion rashly conceived.

Therefore, let knowledge be present to govern zeal. And it is said that zeal was the cause of diligence, because Apollos devoted himself to teaching diligently.

But if that man, not yet being thoroughly and perfectly taught in the gospel, preached Christ so diligently and freely, what excuse can those men hope to have who know more perfectly and fully what he did not yet know, if they do not endeavor as much as is in their power to further and advance the kingdom of Christ?

Luke attributes zeal to the Spirit, because it is a rare and special gift. Nor do I interpret this to mean that Apollos was moved and spurred on by the instinct of his own mind, but rather by the prompting of the Holy Spirit.