Mathias was one of the first to follow our Savior; and he was an eye-witness of all His divine actions up to the very day of the Ascension. He was one of the seventy-two disciples; but our Lord had not conferred upon him the dignity of an apostle. And yet, he was to have this great glory, for it was of him that David spoke, when he prophesied that another should take the bishopric left vacant by the apostasy of Judas the traitor. In the interval between Jesus' Ascension and the descent of the Holy Ghost, the apostolic college had to complete the mystic number fixed by our Lord Himself, so that there might be the twelve on that solemn day, when the Church, filled with the Holy Ghost, was to manifest herself to the Synagogue. The lot fell on Mathias; he shared with his brother-apostles the persecution in Jerusalem, and, when the time came for the ambassadors of Christ to separate, he set out for the countries allotted to him. Tradition tells us that these were Cappadocia and the provinces bordering on the Caspian Sea.
The virtues, labor, and sufferings of St. Mathias have not been handed down to us: this explains the lack of proper lessons on his life, such as we have for the feasts of the rest of the apostles. Clement of Alexandria records in his writings several sayings of our holy apostle. One of these is so very appropriate to the spirit of the present season, that we consider it a duty to quote it. 'It behoves us to combat the flesh, and make use of it, without pampering it by unlawful gratifications. As to the soul, we must develop her power by faith and knowledge.' How profound is the teaching contained in these few words! Sin has deranged the order which the Creator had established. It gave the outward man such a tendency to grovel in things which degrade him, that the only means left us for the restoration of the image and likeness of God unto which we were created, is the forcible subjection of the body to the spirit. But the spirit itself, that is, the soul, was also impaired by original sin, and her inclinations were made prone to evil; what is to be her protection? Faith and knowledge. Faith humbles her, and then exalts and rewards her; and the reward is knowledge.
~from The Liturgical Year, Abbot Gueranger O.S.B. via Catholic Culture