11 “Sion heard of it, and rejoiced”. What did Sion hear? That all His Angels worship Him....For the Church was not as yet among the Gentiles; in Judæa the Jews had some of them believed, and the very Jews who believed thought that they only belonged to Christ: the Apostles were sent to the Gentiles, Cornelius was preached to; Cornelius believed, was baptized, and they who were with Cornelius were also baptized. But ye know what happened, that they might be baptized: the reader indeed has not reached this point, but, nevertheless, some recollect; and let those who do not recollect, hear briefly from me.
The Angel was sent to Cornelius: the Angel sent Cornelius to Peter; Peter came to Cornelius. And because Cornelius and his household were Gentiles, and uncircumcised: lest they might hesitate to give the Gospel to the uncircumcised: before Cornelius and his household were baptized, the Holy Spirit came, and filled them, and they began to speak with tongues. Now the Holy Spirit had not fallen upon any one who had not been baptized: but upon these It fell before baptism. For Peter might hesitate whether he might baptize the uncircumcised: the Holy Spirit came, they began to speak with tongues; the invisible gift was given, and took away all doubt about the visible Sacrament; they were all baptized....What did Sion hear, and rejoice at?
That the Gentiles also had received the word of God. One wall had come, but the corner existed not as yet. The name Sion is here peculiarly given to the Church which was in Judæa. “Sion heard of it, and rejoiced: and the daughters of Judah were glad.” Thus it is written, “The apostles and brethren that were in Judæa heard.” See if the daughters of Judæa rejoiced not. What did they hear? “That the Gentiles had also received the word of God.”...Therefore, “The daughters of Judah rejoiced because of Your judgments, O Lord.” What is, because of Your judgments? Because in any nation, and in any people, he that serves Him is accepted of Him: for He is not the God of the Jews only, but also of the Gentiles.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)