1 The title of the Psalm is, “For her who receives the inheritance.” The Church then is signified, who receives for her inheritance eternal life through our Lord Jesus Christ; that she may possess God Himself, in cleaving to whom she may be blessed, according to that, “Blessed are the meek, for they shall possess the earth.” What earth, but that of which it is said, “You are my hope, my portion in the land of the living”? And again more clearly, “The Lord is the portion of mine inheritance and of my cup.” And conversely the word Church is said to be God's inheritance according to that, “Ask of Me, and I shall give you the heathen for your inheritance.” Therefore is God said to be our inheritance, because He feeds and sustains us: and we are said to be God's inheritance, because He orders and rules us. Wherefore it is the voice of the Church in this Psalm called to her inheritance, that she too may herself become the inheritance of the Lord.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)