NOTES for Act 1:12-26
It is hardly accidental that Luke notes that the distance the apostles walked from the Mount of Olives to Jerusalem was a Sabbath day's journey. From this we can conclude that for the apostles the waiting for Pentecost was a ten-day Sabbath, a time of rest and prayer needed in order to prepare properly to receive what Christ had promised them. The Lord can reveal Himself and His powers at any time, catching us off guard, but it is better if we are ready to meet Him.
Meanwhile, the apostles gather together with the whole community, already numbering about one hundred twenty people, and in their presence, not privately, they decide who will fill the breach left in their ranks by Judas' betrayal. Why is this necessary? Is it only because the number 12 symbolizes fullness and because the apostles are to sit on 12 thrones judging the 12 tribes of Israel? Yes, for those reasons too, but in addition, everyone whom the Lord called to apostleship was especially dear to Him. Judas fell, and now Matthias is to continue those ministries of Judas that the Lord had wanted to entrust to him before his betrayal. A good work being done by an apostate must not stop; it must be continued by another, by one who continues to keep faith.