6 “Like as the arrows in the hand of the mighty one, even so are the children of those that are shot out”. Whence has sprung this heritage, brethren? Whence has sprung so numerous a heritage? Some have been shot out from the Lord's hand, as arrows, and have gone far, and have filled the whole earth, whence the Saints spring. For this is the heritage whereof it is said, “Desire of Me, and I shall give you the heathen for your inheritance, and the uttermost parts of the earth for your possession.” And how does this possession extend and increase unto the world's uttermost parts?
Because, “like as the arrows in the hand of the mighty one,” etc. Arrows are shot forth from the bow, and the stronger the arm which has sent it forth, the farther flies the arrow. But what is stronger than the darting of the Lord? From His bow He sends forth His Apostles: there could not be a spot left where an arrow shot by so strong an arm would not reach; it has reached unto the uttermost parts of the earth. The reason it went no farther was, that there were no more of the human race beyond. For He has such strength, that even if there were a spot beyond, whither the arrow could fly, He would dart the arrow there. Such are the children of those who are shot forth as they that are shot forth....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)