11 In the first book, Theophilus, I wrote about all that Jesus did and taught from the beginning 2 until the day when he was taken up to heaven, after giving instructions through the Holy Spirit to the apostles whom he had chosen. 3 After his suffering he presented himself alive to them by many convincing proofs, appearing to them during forty days and speaking about the kingdom of God.
Matthew Henry's Commentary on Acts 1:1-3
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.