"In those days, Peter stood up in the midst of the disciples and said..." As the fiery spirit to whom the flock was entrusted by Christ and as the leader in the band of the apostles, Peter always took the initiative in speaking: "My brothers, we must choose from among our number." He left the decision to the whole body, at once augmenting the honor of those elected and avoiding any suspicion of partiality.
Did not Peter then have the right to make the choice himself? Certainly he had the right, but he did not want to give the appearance of showing special favor to anyone. "And they nominated two," we read, "Joseph, who was called Barsabbas and surnamed Justus, and Matthias." He himself did not nominate them; all present did. But it was he who brought the issue forward, pointing out that it was not his own idea but had been suggested to him by a scriptural prophecy.
And they all prayed together, saying: "You, Lord, know the hearts of men; make your choice known to us. You, not we." Appropriately they said that he knew the hearts of men, because the choice was to be made by him, not by others.
They spoke with such confidence, because someone had to be appointed. They did not say "choose" but "make known to us" the chosen one; "the one you choose," they said, fully aware that everything was being preordained by God.
-from a homily on the Acts of the Apostles by Saint John Chrysostom
O Glorious Saint Matthias, in God's design it fell upon you to take the place of the unfortunate Judas who betrayed his Master. You were selected by the twofold sign of the uprightness of your life and the call of the Holy Spirit. Obtain for us the grace to practice the same uprightness of life and to be called by that same Spirit to wholehearted service of the Church. Then after a life of zeal and good works let us be ushered into your company in heaven to sing forever the praises of Father, Son, and Holy Spirit. Amen.