Albert Barnes 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)

And when they had prayed. The event that followed was regarded by them as evidence that God heard their prayer.

The place was shaken. The word that is translated "was shaken" commonly denotes violent agitation, such as the raging of the sea, the convulsion of an earthquake, or trees shaken by the wind (Matthew 11:7; Acts 16:26; Hebrews 12:26).

The language here is suited to express the idea of an earthquake. It is not stated whether the motion was confined to the house where they were. They probably regarded this as an answer to their prayer, or as evidence that God would be with them, for several reasons:

1. Because it was sudden and violent, and was not produced by any natural causes.
2. Because it occurred immediately, while they were seeking divine direction.
3. Because it was an exhibition of great power, and was evidence that God could protect them.
4. Because a convulsion so great, sudden, and mighty was suited at that time to awe them with a proof of the presence and power of God.

A similar instance of an answer to prayer by an earthquake is recorded in Acts 16:25-26 .

Furthermore, among the Jews an earthquake was very properly regarded as a striking and impressive proof of the presence of Jehovah, as seen in Isaiah 29:6 and Psalm 68:8: The earth shook, the heavens also dropped at the presence of God: even Sinai itself was moved at the presence of God, the God of Israel.

See also the sublime description in Habakkuk 3:6-11 . Among the heathen, an earthquake was similarly regarded as proof of the presence and favor of a deity (see Virgil, Aeneid 3.89).

They were all filled, etc. (See the notes on Acts 2:4).

Their being filled with the Holy Ghost, in this instance, denotes their being inspired with confidence or boldness, rather than being endowed with new powers, as in Acts 2:4.

"Holy Ghost" (or "Spirit"). They spoke the word (Acts 4:29).