In vs. 24 they all prayed and then proclaimed that the “Lord knew everyone’s heart” (NRSV). They then beseech the majestic wisdom of God and the Holy Spirit to “show” them which one He would choose, Justus or Matthias. The “respectable precedent in Hebrew sacred history” of casting lots was used for God to overrule their opinion since either man was probably worthy of the calling.
F.F. Bruce noted that there is no “NT example of this procedure after the descent of the Spirit on the day of Pentecost; this may or may not be significant.” This is a unique happening in the literary corpus of the text of Scripture. In their minds, they were essentially leaving it up to God. Bruce also notes Proverbs 16:33 which possibly influenced this custom or occasion in Acts 1:6:
Proverbs 16:33, The lot is cast into the lap, but its every decision is from the LORD. NIV
One commentator-Kenneth O. Gangel-suggests that the casting of "lots" by the Disciples is a “sovereign election…they prayed directly for God’s will and he gave it.” Notice, there does not seem to be any wrongdoing in the method’s and processes of the Disciples. These were men bereft of their Messiah, betrayed and even offered up by one of their own—Judas Iscariot the "assassin" from Kerioth. Their using of lots was possibly an indicator that they were at least willing to allow God to overrule what they, even as a collective, might have wanted.
Later we realize that the number 12 was hardly a number held to since Paul and Barnabas both are added to the number. Even when James, the brother of Jesus was killed by Herod (12:1) there was no casting of lots. Here we see the only reconstitution of the 12 given us in Scripture.
I think there is a pattern here. I am not sure exactly how much divinity we should invest into all our choices but I do believe that we still have the capacity for human error. I believe we must pray and be willing for God to intervene. That is the attitude of the Disciples, at the very least.
Gangel, Kenneth O. Holman New Testament Commentary-Acts of the Apostles © 1998 Broadman & Holman Publishers Nashville, Tennessee pg. 10
Bruce, F.F. The New International Commentary on the New Testament-The Book of Acts Wm. B. Eerdman Publishing Company Grand Rapids, Michigan, USA Reprinted February 1980 pg. 51