Why did Peter believe it was "necessary" to choose someone to take Judas" place? Evidently he remembered Jesus" promise that the12disciples would sit on12thrones in the messianic kingdom judging the12tribes of Israel ( Matthew 19:28; Luke 22:30; cf. Revelation 21:14). To be as qualified for this ministry as the other11disciples the twelfth had to have met the conditions Peter specified. [source][source][source]
"In Acts 1:21 Peter speaks not of being with Jesus but of going with him on his journeys.... This emphasis on journeying with Jesus, particularly on his final journey to the cross, suggests that the apostolic witnesses are qualified not simply because they happened to be present when something happened and so could report it, like witnesses to an accident. Rather they have been taught and trained by Jesus for their work. They shared Jesus" life and work during his mission. In the process they were tested and discovered their own defects. That discovery may also be part of their preparation. The witness of the Galileans does not arise from casual observation. They speak out of a life and mission shared with Jesus, after being taught and tested. From this group the replacement for Judas is chosen." [1][source]
"The expression "went in and out among us" [2] is a Semitic idiom for familiar and unhindered association (cf. Deuteronomy 31:2; 2 Samuel 3:25; Psalm 121:8; Acts 9:28)." [3][source]
Having been a witness to Jesus Christ"s resurrection was especially important. The apostles prepared so that if Jesus Christ returned very soon and set up His kingdom on the earth they would be ready. Often in biblical history God replaced someone who proved unworthy with a more faithful steward (e.g, Zadok for Ahithophel, Shebna for Eliakim, Samuel for Samson, David for Saul, et al.). [source][source][source]
These two verses provide the basis for distinguishing a technical use of "apostle" from the general meaning of the word. By definition an apostle (from apo stello, to send away) is anyone sent out as a messenger. Translators have frequently rendered this word "messenger" in the English Bible. Barnabas, Paul"s fellow workers, James , and Epaphroditus were apostles in this sense ( Acts 14:4; Acts 14:14; 2 Corinthians 8:23; Galatians 1:19; Philippians 2:25). Every Christian should function as an apostle since Christ has given us the Great Commission. Nevertheless, the Twelve were apostles in a special sense. They not only went out with a message, but they went out having been personally discipled by Jesus Christ during His earthly ministry. They were the official apostles, the apostles who occupied the apostolic office ( Acts 1:20) that Jesus established when He first chose and sent out the Twelve ( Luke 6:13). As we shall see, Paul was also an official apostle though he had not been personally discipled by Jesus as the Twelve had. [source][source][source]
This address of Peter ( Acts 1:16-21) is the first of some23or24speeches that Luke reported in Acts. About one third of the content of Acts is speeches. [4] This one is an example of deliberative rhetoric, in which the speaker seeks to persuade his hearers to follow a certain course of action in the near future. [5] How accurate did Luke attempt to be when he recorded the speeches in Acts?[source]
"To an extent, of course, all the speeches in Acts are necessarily paraphrastic, for certainly the original delivery contained more detail of argument and more illustrative material than Luke included-as poor Eutychus undoubtedly could testify ( Acts 20:7-12)! Stenographic reports they are not, and probably few ever so considered them. They have been reworked, as is required in any prcis, and reworked, moreover, in accord with the style of the narrative. But recognition of the kind of writing that produces speeches compatible with the narrative in which they are found should not be interpreted as inaccurate reporting or a lack of traditional source material. After all, a single author is responsible for the literary form of the whole." [6][source]