Expositor's Bible Commentary Commentary Acts 4:31

"And when they had prayed, the place was shaken wherein they were gathered together; and they were all filled with the Holy Spirit, and they spake the word of God with boldness." — Acts 4:31 (ASV)

As a sign of God’s approval, Luke informs us that “the place where they were meeting was shaken” (cf. Exodus 19:18; Isaiah 6:4) and “they were all filled with the Holy Spirit” (cf. comments on v.8). And with such motivation and divine enablement, their prayer was answered: they “spoke the word of God boldly” (i.e., with confidence).