This is from the Douay-Rheims. You have to read it in the context of the whole Psalm, also the Douay translation is very literal and not necessarily the best. However, the Psalm speakes basically of the foolishness of the unconverted man, whose end will be no better than the common beasts ( even worse). So don’t live like a beast who does not have an intellect and free will but is guided solely by his passions. If we live by our passions, forgetting God and our final end, it is as though we were no better than wild beasts who have no knowledge of their final end. Augustine has some commentary here :.
“He shall enter even unto the generations of his fathers” (verse 19): that is, he shall imitate his fathers. For the unrighteous, that now are, have brothers, have fathers. Unrighteous men of old, are the fathers of the present; and they that are now unrighteous, are the fathers of unrighteous posterity: just as the fathers of the righteous, the righteous of old, are the fathers of the righteous that now are; and they that now are, are the fathers of them that are to be. The Holy Spirit hath willed to show that righteousness is not evil when men murmur against her: but these men have their father from the beginning, even to the generation of their fathers. Two men Adam begat, and in one was unrighteousness, in one was righteousness: unrighteousness in Cain, righteousness in Abed Unrighteousness seemed to prevail over righteousness, because Cain unrighteous slew Abel righteous(4) in the night. Is it so in the morning? Nay, “but the righteous shall reign over them in the morning.”(5) The morning shall come, and it shall be seen where Abel is, and where Cain. So all men who are after Cain, and so all who are after Abel, even unto the end of the world. “He shall enter even unto the generations of his fathers: even to eternity he shall not see light.” Because even when he was here, he was in darkness, taking pleasure in false goods, and not loving real goods: even so he shall go hence into hell: from the darkness of his dreams the darkness of torments shall receive him. Therefore, “even to eternity he shall not see light.” But wherefore this? What he hath written in the middle of the Psalm,(6) the same also he hath writ at the end: “Man, though he was in honour, understood not, was compared to the beasts without sense, and was made like to them” (verse 20). But ye, brethren, consider that ye be men made after the image and likeness of God. The image(7) of God is within, is not in the body; is not in these ears which ye see, and eyes, and nostrils, and palate, and hands, and feet; but is made nevertheless
8) wherein is the intellect, wherein is the mind, wherein the power of discovering truth, wherein is faith, wherein is your hope, wherein your charity, there God hath His Image: there at least ye perceive and see that these things pass away; for so he hath said in another Psalm, “Though man walketh in an image, yet he is disquieted in vain: he heapeth up treasures, and knoweth not for whom he shall gather them.”(9) Be not disquieted, for of whatsoever kind these things be, they are transitory, if ye are men who being in honour understand. For if being men in honour ye understand not, ye are compared to the beasts without sense, and are made like to them.
