Two things strike me as I read this sentence. One is great power, and the other is great grace. It seems to be possible to testify to the resurrection of the Lord Jesus without great power, and it seems to be possible, too, to have a body of believers who do not have great grace resting upon them.
There was something special that preceded this statement: “Now the company of those who believed were of one heart and one soul, and no one said that any of the things which he possessed was his own, but they had everything in common” (Acts 4:32).
People were not attached to their possessions, and they were of one heart. Maybe this is why there was great power and great grace? No, this was another evidence of that power and grace.
Here is the reason in verse 31: “And when they had prayed, the place in which they were gathered together was shaken; and…