I have a little concern here:
“Therefore it is necessary to choose one of the men who have been with us the whole time the Lord Jesus went in and out among us, beginning from John’s baptism to the time when Jesus was taken up from us. For one of these must become a witness with us of his resurrection.” So they proposed two men: Joseph called Barabbas (also known as Justus) and Mathias. (Acts 1:21-23) This means that there were more than 12 disciples that had been with Jesus all the time and were eyewitness since his Baptism and ascend to heaven. But why does the Bible only dwell on twelve?
You’re correct. There were many more than 12 disciples. The word means student or pupil, and Jesus had numerous followers of this type. The second time he sent disciples out to bring the good news to Israel he sent 72, not just 12 like He had the first time. (Luke 10:1)
The 12 are featured because they were the Lord’s closest associates among those who were with Him throughout His ministry on Earth. And even among them, He had an inner circle consisting of Peter, James, John, and sometimes Andrew.