St.Matthias could have been one of the seventy-two disciples who followed Jesus in His Ministry and who had been sent out in pairs by Jesus Himself to the places where He would be visiting. (Lk. 10, 1-23) Jesus had chosen twelve Apostles, but Judas had ceased to be one of them. When Jesus was taken up to heaven (Ascension) the remaining Apostles, under the leadership of Peter, felt that they should replace Judas, so that the number of the Apostles should remain twelve, as Jesus had determined.
Some scholars point out that the number twelve was an important number for the Chosen People as it had a strong reference to the twelve tribes of Israel.
Peter addressed about one hundred and twenty people that were gathered in the ‘Upper Room’ for prayer and reflection, before the choice of the twelfth apostle. A criteria for selection was set out. The person chosen had to be one of the disciples who had travelled with Jesus throughout His Ministry, since His Baptism by John in the Jordan and having been witness to His appearances after the Resurrection and to His Ascension.
There were two disciples who qualified fully: Matthias and Joseph Barsabbas. All those present decided not to take a vote but to cast lots after praying to God for the choice of His will. Each name was written on two separate stones that were placed in a container, which was shaken so that one stone would fall out. The stone bearing the name of Matthias fell out. He was then accepted as one of the Twelve, and later, together with the rest of the Apostles, received the Holy Spirit on Pentecost.
Matthias began to teach the Risen Christ, not only in Jerusalem and throughout Judea but he also set out on a missionary journey to Cappadocia ( in central modern-day Turkey). He was persecuted by those who did not want to accept Jesus Christ and He was finally martyred (around 64 AD) in Colchis, a place in the Caucasus Mountains. There are different accounts of his martyrdom. He was either crucified or beheaded, a faithful apostle of Jesus Christ till the end.