Why did the Spirit not come while Jesus was present, or immediately on His departure? Because it was fitting that they should become desirous of grace, and then at length receive it. For we are then most awakened towards God, when difficulties press upon us. It was necessary in the meantime that our human nature should appear in Heaven, and the covenants be completed, and then the Spirit should come, and pure joys be experienced. Notice also what requirement Jesus imposed upon His apostles of being at Jerusalem, in that He promised that the Spirit should there be given them. For if they should again run away after His resurrection by this expectation, Jesus kept them all there together. But He says: "...until you are clothed with power from on high.” He did say when, in order that they may be constantly watchful.
But observe, that the Lord shows us the promised rewards. He had promised the resurrection of the body; He rose from the dead, and conferred with His disciples for forty days. It is also promised that we shall be caught up in the clouds through the air. But you will say, How does this concern me? Because you also shall be taken up in like manner into the clouds. For your body is of like nature to His body.