That's what the book of Acts is really called -- The Acts of the Holy Spirit. If this book were still being written today, perhaps we'd be in chapter 2000 or so by now. Would you be in it? Would someone we know be in it? Would our church be a part of it? The Holy Spirit is surely working today amongst God's people. I think it's cool how a part of the body we call "Charismatics" and another part called "Pentecostals" are actually looking for and expecting God's Spirit to move within them. I think that kind of expectation is important. God will often use those that don't expect it, but for those that are willing, waiting, and ready, perhaps they'll see more "activity" ... who knows?
It's cool that Luke wrote the Book of Acts, because he was a doctor and he's so good with details. He can be gross at times, like the verse where he describes Judas' death: "...there he fell headlong, his body burst open and all his intestines spilled out." Yeah, thanks, Luke!
Peter stood up and proposed that they choose another apostle, so they will have 12 again. He cites the book of Psalms (109:8):
"May another take his place of leadership."
I never would have thought that the hidden meaning behind that Psalm was for Judas, but that is how many gems of truth are "hidden" in the Old Testament, and "revealed" in the New.
It's interesting how they decided to pick from between Justus and Matthias. They prayed:
"Lord, You know everyone's heart. Show us which of these two You have chosen to take over this apostolic ministry, which Judas left to go where he belongs."
They might've been pretty pretty leary over choosing someone, when they saw how the "wrong choice" could lead to betrayal. Maybe they were afraid of choosing another Judas. Either way, they knew that it was a very important decision, and they couldn't decide on their own. So they "left it up to God" by praying that prayer and then casting lots. The lot fell to Matthias.
Isn't that interesting? How would you feel if Billy Graham, Rick Warren, Chuck Smith, and James Robison were on television, hosting a ministry time, and one of them said, "We need to decide such and such." Then they joined in prayer, asking God to show them the answer, and then they rolled a pair of dice. it would probably freak our culture out, wouldn't it?