What to do with a vision…
And while Peter was earnestly revolving the vision in his mind and meditating on it, the [Holy] Spirit said to him, Behold, three men are looking for you!
Paul had a vision that he did not understand, so he pondered and meditated on it. In this case, Paul received the understanding quickly. The lesson from the vision instructed him in a way that he could go with people he would never have gone with prior to the vision.