John Calvin Commentary Acts 18:26

"and he began to speak boldly in the synagogue. But when Priscilla and Aquila heard him, they took him unto them, and expounded unto him the way of God more accurately." — Acts 18:26 (ASV)

Whom, when Priscilla. By this it appears how far Priscilla and Aquila were from self-love and from envying another's virtue, in that they communicated these things informally and privately to an eloquent man, which he could afterward declare publicly. They did not excel in the same grace in which he excelled, and perhaps they might have been looked down upon in the congregation. Moreover, they most diligently helped him, whom they saw was better equipped with both eloquence and proficiency with the Scripture, so that they kept silent, and he alone was heard.

Again, Apollos showed no small modesty in that he allowed himself to be taught and instructed not only by a craftsman but also by a woman. He was mighty in the Scripture and surpassed them; but concerning a more complete understanding of the kingdom of Christ, those who might have seemed to be scarcely fit ministers polished and refined him. Also, we see that at that time women were not as ignorant of the word of God as the Papists portray them, since we see that one of the Church's foremost teachers was instructed by a woman. Nevertheless, we must remember that Priscilla carried out this function of teaching in her own house, so that she would not overturn the order prescribed by God and nature.