7 Then what? “Wherefore have You thrown down her enclosure?”. Now ye see the overthrow of that nation of the Jews: already out of another Psalm you have heard, “with axe and hammer they have thrown her down.” When could this have been done, except her enclosure had been thrown down. What is her enclosure? Her defence. For she bore herself proudly against her planter. The servants that were sent to her and demanded a recompense, the husbandmen they scourged, beat, slew: there came also the Only Son, they said, “This is the Heir; come, let us kill Him, and our own the inheritance will be:” they killed Him, and out of the vineyard they cast Him forth. When cast forth, He did more perfectly possess the place whence He was cast forth. For thus He threatens her through Isaiah, “I will throw down her enclosure.” Wherefore? “For I looked that she should bring forth grapes, but she brought forth thorns.” I looked for fruit from thence, and I found sin. Why then do you ask, O Asaph, “Why have You thrown down her enclosure?” For do you not know why? I looked that she should do judgment, and she did iniquity. Must not her enclosure needs be thrown down? And there came the Gentiles when the enclosure was thrown down, the vineyard was assailed, and the kingdom of the Jews effaced. This at first he is lamenting, but not without hope. For of directing the heart he is now speaking, that is, for the “Assyrians,” for “men directing,” the Psalm is. “Wherefore have You thrown down her enclosure: and there pluck off her grapes all men passing along the way.” What is “men passing along the way?” Men having dominion for a time.
8. “There has laid her waste the boar from the wood”. In the boar from the wood what do we understand? To the Jews a swine is an abomination, and in a swine they imagine as it were the uncleanness of the Gentiles. But by the Gentiles was overthrown the nation of the Jews: but that king who overthrew, was not only an unclean swine, but was also a boar. For what is a boar but a savage swine, a furious swine? “A boar from the wood has laid her waste.” “From the wood,” from the Gentiles. For she was a vineyard, but the Gentiles were woods. But when the Gentiles believed, there was said what? “Then there shall exult all the trees of the woods.” “The boar from the wood has laid her waste; and a singular wild beast has devoured her.” “A singular wild beast” is what? The very boar that laid her waste is the singular wild beast. Singular, because proud. For thus says every proud one, It is I, it is I, and no other.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)