This passage occurs for Ascension in the RCL, all three years; sometimes this is marked on a Thursday other times it takes the place of Easter 7.
Summary: Normally good-byes are sad. But not the Ascension! Luke wants to point out a few things about the ascension. Namely that it is a commissioning; a celebration; and a crescendo. A closer look at the Greek suggests this often overlooked story is vitally important for the Christian understanding of God in Christ Jesus. In fact, as I read Luke's account of the Ascension this year (2013) I am realizing I have improperly truncated the Gospel. The Gospel must include forgiveness and resurrection but also the sending of the Holy Spirit who brings us into the witness of the Gospel. But if that just sounds too much for your Lutheran piety, you can go with this: Jesus knows that preaching forgiveness will get us into trouble because the world cannot handle law and Gospel.
μαρτυρες ("witness", from μαρτυς, 24:48) The Greek word there for witness is "martyros," from which we get our word Martyr. It originally had a simple legal connotation, as in give testimony, or generally, to speak on someone's behalf. Yet in the Christian context, it very quickly came to mean suffer for this proclamation, including Jesus himself. So Jesus says (literally), "You are martyrs of these things." This is the ultimate commissioning: You will go out and testify to the resurrection and forgiveness of sins and be persecuted for it.
χαρας ("joy", from χαρα, 24:52) Luke uses this word more than other authors. It is significant that worship of the ascended Christ still fills the believers with great joy. Luke makes the point: Just because Jesus isn't here on earth doesn't mean we cannot worship him. In fact, worship of the risen (and ascended Christ) still fills the believers with joy. Jesus ascension means unlimited access instead of only local contact; hence the possibility of a universal church.
προσκυνησαντες ("worship", προσκυνεω, 24:52) For all of the times Luke has Jesus praying, this is the only instance where people are worshiping in his Gospel. The only other mention of the verb is in the temptation of Christ where Jesus declares we must worship God alone. For Luke, the ascension confirms Jesus' divinity in a way that allows the disciples to worship him as God in way even his resurrection did not. The ascension completes his first mission on earth: his suffering, his resurrection and his commissioning. Now he shall return to be exalted and come again in glory.
διηνοιξεν ("open", 24:45) We saw this verb last week in Acts account of Lydia's Baptism. It is interesting that this word is associated in Acts and Luke with understanding the Word. It also suggests the need for proclamation, because the Scriptures need to be opened. They are not self-explanatory.
καθισατε ("sit", καθιζω, 24:49) The disciples are told to "sit" until the Holy Spirit comes. Part of the Christian life is waiting.
δυναμιν ("power" from δυναμις. 24:49) This word comes into English as dynamite. Christ calls us to be both the martrys and dynamite for the world. The two seem related in tragic ways; yet, Christ does not call us to cause suffering in others, but simply to suffer for others as the world persecutes the news of forgiveness and resurrection.
Grammar concept: hendiadys; or in this case, hendiatris
Hendiadys refers to the literary device of using two words to mean one thing. For instance: "formless and void" of Genesis 1 means "a whole lot of nothing!" or perhaps more accurately, "chaos."
In this case, Jesus refers to Scriptures by calling them: Moses, Prophets and Psalms. Here he is referring to all of the OT, not simply Gen-Deut; 12 prophets and Psalms. He is laying out the Tanakh (Torah, Prophets and Writings) division of Scripture.