7 Perhaps the Apostles themselves are styled the sons of those who have been shaken out, the sons of the Prophets. For the Prophets comprised closed and covered mysteries: they were shaken, that they might come forth thence manifestly....Except the prophecy involved were sifted with diligence, would the concealed meanings come forth unto us? All these meanings were therefore closed before the Lord's advent. The Lord came, and shook out these hidden meanings, and they were made manifest; the Prophets were shaken out, and the Apostles were born. Since then they were born of the Prophets who had been shaken out, the Apostles are sons of those that were shaken out. They, placed as the arrows in the hand of the giant, have reached the uttermost parts of the earth....The Apostles the sons of the Prophets have been like as the arrows in the hand of a mighty one. If He is mighty, He has shaken them out with a mighty hand; if He has shaken them out with a mighty hand, they whom He has shaken forth have arrived even at the uttermost parts of the earth.
8. “Blessed is the man who has filled his desire from them”. Well, my brethren, who fills his desire from them? Who loves not the world. He who is filled with the desire of the world, has no room for that to enter which they have preached. Pour forth what you carry, and become fit for that which you have not. That is, you desire riches: you can not fill your desire from them: you desire honours upon earth, you desire those things which God has given even unto beasts of burden, that is, temporal pleasure, bodily health, and the like; you will not fulfil your desire from them....“He shall not be ashamed, when he speaks with his enemies in the gate.” Brethren, let us speak in the gate, that is, let all know what we speak. For he who chooses not to speak in the gate, wishes what he speaks to be hidden, and perhaps wishes it to be hidden for this reason, that it is evil. If he be confident, let him speak in the gate; as it is said of Wisdom, “She cries at the gates, at the entry of the city.” As long as they hold unto righteousness in innocency, they shall not be ashamed: this is to preach at the gate. And who is he who preaches at the gate? He who preaches in Christ; because Christ is the gate whereby we enter into that city....They, therefore, who speak against Christ, are without the gate; because they seek their own honours, not those of Christ. But he who preaches in the gate, seeks Christ's honour, not his own: and, therefore, he who preaches in the gate, says, Trust not in me; for you will not enter through me, but through the gate. While they who wish men to trust in themselves, wish them not to enter through the gate: it is no marvel if the gate be closed against them, and if they vainly knock for it to be opened.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)