They unlocked their door
“It is noteworthy [in Acts chapter 2] that the disciples, who appear to have been hiding away from their enemies in the spirit of John 20:19, immediately became different people. They unlocked their door, and went down to the most public place they could find and there preached Jesus boldly. This change from cringing cowards to fearless preachers was permanent. We read of Christians making all sorts of mistakes afterwards, and they are far from being perfect. But we do not again read of them hiding away for fear of men. The Spirit altered all that. From now on they became fearless vehicles of the Spirit in proclaiming to men the message of the gospel.”
Leon Morris, Spirit of the Living God (Chicago, 1960), page 53.