This sign was a reversal of God’s judgment at the Tower of Babel. God’s judgment scattered and separated those people then, now He was uniting His people in the Spirit. At Babel no one could understand anyone else, but at Pentecost everyone could understand and hear God’s praises.
Acts Wednesday: Chapter 18, Apollos
Apollos had everything you could possibly want to be effective: he had education, talent, skill and experience. But until Apollos had the Holy Spirit, his ministry was not effective.