A second purpose for these forty days was to command the disciples: “….being seen by them during forty days and speaking of the things pertaining to the Kingdom of God. And being assembled together with them, He commanded them not to depart from Jerusalem, but to wait for the Promise of the Father….” Acts 1:3-4). It is obvious that the disciples did not understand many things about the Messiah and His kingdom before His death and Jesus could now speak more clearly about the cross and its relationship to the kingdom of God. We are not given any particulars concerning the kingdom Jesus taught them.
However, Paul’s statement in Ephesians may help us understand some of the things: “How that by revelation He made known to me the mystery (as I have briefly written already, by which, when you read, you may understand my knowledge in the mystery of Christ), which in other ages was not made known to the sons of men, as it has now been revealed by the Spirit to His holy apostles and prophets: that the Gentiles should be fellow heirs, of the same body, and partakers of His promise in Christ through the gospel, of which I became a minister according to the gift of the grace of God given to me by the effective working of His power” (3:2-7).
A third purpose may have been to correct some misunderstandings. “Therefore, when they had come together, they asked Him, saying, “Lord, will You at this time restore the kingdom to Israel?” (Acts 1:6).
I believe the reason the disciples used the phrase “restore the kingdom to Israel” is because they were anticipating a nationalistic kingdom of earthly glory as in the days of David and Solomon. Jesus said, “It is not for you to know times or seasons which the Father has put in His own authority. But you shall receive power when the Holy Spirit has come upon you; and you shall be witnesses to Me in Jerusalem, and in all Judea and Samaria, and to the end of the earth” (Acts 1:7-8).
They needed to forget the idea of an immediate defeat of Rome and the restoration of the Jewish kingdom and concentrate on the mission He had given them: And He said to them, “Go into the entire world and preach the gospel to every creature. He who believes and is baptized will be saved; but he who does not believe will be condemned” (Mark 16:15-16)
May the God of our Salvation, Who's Throne in Glory, be praised.