Why was the hand of the Lord with these preachers?
God was ready to move the Gospel out to the Gentile world, so His hand was with these preachers. He had begun this by saving Saul, sending Peter to Cornelius, and giving Saul the revelation of the mysteries; therefore Jewish preachers began speaking to Greeks, preaching the Lord Jesus, and a great number believed.
Les teaches that the hand of the Lord was with these preachers because God was ready to move things out to the Gentile world. This was a change in venue and a change in modus operandi: the Jewish believers had been preaching to Jews only, but now they began to speak to Greeks and preach the Lord Jesus. God had started the ball rolling toward the Gentile world when He saved Saul, and He speeded it up when He sent Peter up to Cornelius. By this point Saul had already returned from his three years of learning and the revelation of the mysteries, so the Gospel was ready to go out to the Gentiles. Verse 21 confirms that the hand of the Lord was with them, and a great number believed and turned unto the Lord.