2 Till the day when he was taken up to heaven after he had given his orders, through the Holy Spirit, to the Apostles of whom he had made selection: 3 And to whom he gave clear and certain signs that he was living, after his death; for he was seen by them for forty days, and gave them teaching about the kingdom of God: 4 And when they were all together, with him, he gave them orders not to go away from Jerusalem, but to keep there, waiting till the word of the Father was put into effect, of which, he said, I have given you knowledge:
Matthew Henry's Commentary on Acts 1:2-4
Commentary on Acts 1:1-5
(Read Acts 1:1-5)
Our Lord told the disciples the work they were to do. The apostles met together at Jerusalem; Christ having ordered them not to depart thence, but to wait for the pouring out of the Holy Spirit. This would be a baptism by the Holy Ghost, giving them power to work miracles, and enlightening and sanctifying their souls. This confirms the Divine promise, and encourages us to depend upon it, that we have heard it from Christ; for in Him all the promises of God are yea and amen.