5 As if you should ask again, who are the beloved? “Lo, children, the reward of the fruit of the womb, are an heritage of the Lord”. Since he says, “fruit of the womb,” these children have been born in travail. There is a certain woman, in whom what was said unto Eve, “in sorrow shall you bring forth children,” is shown after a spiritual manner. The Church bears children, the Bride of Christ; and if she bears them, she travails of them. In figure of her, Eve was called also “the Mother of all living.” He who said, “My little children, of whom I travail in birth again, until Christ be formed in you,” was among the members of her who travails. But she travailed not in vain, nor brought forth in vain: there will be a holy seed at the resurrection of the dead: the righteous who are at present scattered over the whole world shall abound. The Church groans for them, the Church travails of them; but in that resurrection of the dead, the offspring of the Church shall appear, pain and groaning shall pass away....
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)