Matthew Henry Commentary Acts 19:8-12

"And he entered into the synagogue, and spake boldly for the space of three months, reasoning and persuading [as to] the things concerning the kingdom of God. But when some were hardened and disobedient, speaking evil of the Way before the multitude, he departed from them, and separated the disciples, reasoning daily in the school of Tyrannus. And this continued for the space of two years; so that all they that dwelt in Asia heard the word of the Lord, both Jews and Greeks. And God wrought special miracles by the hands of Paul: insomuch that unto the sick were carried away from his body handkerchiefs or aprons, and the evil spirits went out." — Acts 19:8-12 (ASV)

When arguments and persuasions only harden people in unbelief and blasphemy, we must separate ourselves and others from such unholy company. God was pleased to confirm the teaching of these holy men of old, so that if their hearers did not believe them, they might believe the works.