We don’t really know much about St. Matthias. We have no idea what kind of holiness of life he led that led to his being nominated as one of two possibilities to take Judas’s position among the Twelve Apostles.
What is striking about the selection of St. Matthias though is that this is the first of the Apostles that was not selected by Jesus. Jesus selected all of the original Twelve, but Matthias is the first to be selected by the fledgling Church on the authority passed on by Jesus himself. They act not on their own, but on the authority of Jesus, being led by the Holy Spirit for the glory of God the Father.
That same process has been repeated through the ages, over and over again, to select men to be bishops, priests and deacons, and men and women for religious communities. It is the forerunner of the process of discernment that the Church uses in so many situations.
Today we praise God for the Twelve Apostles, of which Matthias was one. We praise God for the authority of the Apostles which has echoed through the ages giving guidance to the Church. We praise God for the gift of the Holy Spirit who is active in all our decision-making