4 Of this people too, of the people of the Jews, were they, who when Peter was speaking, setting forth the Passion, and Resurrection, and Divinity of Christ (after that the Holy Ghost had been received, when all they on whom the Holy Ghost had come, spoke with the tongues of all nations), being pricked in spirit as they heard him, sought counsel for their salvation, understanding as they did that they were guilty of the Blood of Christ; because they had crucified, and slain Him, in whose name though slain by them they saw such great miracles wrought; and saw the presence of the Holy Ghost.
And so seeking counsel they received for answer; “Repent, and be baptized every one of you, in the name of our Lord Jesus Christ, and your sins shall be forgiven you.” Who should despair of the forgiveness of his sins, when the crime of killing Christ was forgiven to those who were guilty of it? They were converted from among this people of the Jews; were converted, and baptized. They came to the Lord's table, and in faith drank that Blood, which in their fury they had shed. Now in what sort they were converted, how decidedly, and how perfectly, the Acts of the Apostles show.
“For they sold all that they possessed, and laid the prices of their things at the Apostles' feet; and distribution was made unto every man according as he had need; and no man said that ought was his own, but they had all things common.” And, “They were,” as it is written, “of one heart and of one soul.” Lo here are the sheep of whom He said, “I am not sent but unto the lost sheep of the house of Israel.” For to them He exhibited His Presence, for them in the midst of their violence against Him He prayed as He was being crucified, “Father, forgive them, for they know not what they do.” The Physician understood how those frenzied men were in their madness putting the Physician to death, and in putting their Physician to death, though they knew it not, were preparing a medicine for themselves.
For by the Lord so put to death are all we cured, by His Blood redeemed, by the Bread of His Body delivered from famine. This Presence then did Christ exhibit to the Jews. And so He said, “I am not sent, but unto the lost sheep of the house of Israel;” that to them He might exhibit the Presence of His body; not that He might disregard, and pass over the sheep which He had among the Gentiles.
Source: Sermons on Selected Lessons of the New Testament (New Advent)