Probably the most lucid example of how religions both change drastically, and yet remain meaningful, is right here in James Kugel’s two pages on Psalm 23. Kugel, himself an Orthodox Jew and an astonishing scholar, shows that the life of any scripture precludes its being owned by any one religious, interpretive, or scholarly community. In this case, the real Psalm 23 is of course all of them:

For the case of the Psalms is, in miniature, the case of the whole Bible. We know now, better than ever before, what the Psalms originally meant and why they were written. But is that original meaning to be decisive? If, even within the biblical period, the Psalms came to mean something else—if people prayed the same words in a setting different from the intended one and with a different meaning, and if they have continued to do so for more than twenty centuries since—does it really matter that the original authors did not mean for their words to be used and understood in the way that we use and understand them?….

      For example, despite the beauty of the old King James translation of Psalm 23, many modern Bibles have found themselves obliged to abandon its key elements: the basic understanding of the psalm as embodied in that seventeenth-century translation is no longer acceptable to modern scholars. Consider, for example, the psalm’s last line in the King James Version: “Surely goodness and mercy shall follow me all the days of my life: and I will dwell in the house of the Lord for ever.”

      At some point in this psalm’s history, the phrase “dwell in the house of the Lord forever” came to be understood as a reference to life after death. This was in part because of the psalm’s earlier reference to walking “through the valley of the shadow of death”—that shadow extends over all the words that follow. (And if one walks through that valley, getting to its other side, this implies that one arrives at what lies beyond death.) Moreover, the psalm’s reference to dwelling “in the house of the Lord for ever” suggests an unlimited length of time, going on even after “all the days of my life” (mentioned in the previous clause) are over. So it was that Psalm 23 came to be taken as the psalm in the Psalter that holds out the clear hope for life after death; among other functions, it became a staple of funeral services.

      Most contemporary scholars reject this understanding. To begin with, the “valley of the shadow of death” seemed to be a misreading (and misdivision) of the original Hebrew text: “a very dark valley” or “valley of darkness” is closer to what the psalm really says. And it does not say “through” that valley; the Hebrew preposition means only “in.” As for the psalm’s last verse, the words translated “for ever” really only mean “for a length of days” or “for a long time.” It seems more like a reaffirmation, rather than an extension of, “all the days of my life.” (That is why most modern translations render this phrase not as “forever” but “my whole life long” or the like.) As for “the house of the Lord,” everywhere else in the Hebrew Bible this means the temple. One certainly could not be buried in the temple and so dwell there after death: such corpse defilement would render the temple utterly unfit for God’s presence….

      Which is the real Psalm 23? The one that talks about life after death, or the other one? And in a broader sense, what are we to think of the Psalms today, now that we know that, far from being the personal lyrics of King David, scribbled down by a prophetlike servant of God in time of trouble or celebration, they are mostly cultic pieces penned by anonymous temple functionaries, studded with conventional phrases and themes and worded in a one-size-fits-all vocabulary that was designed to give worshippers the feeling of specificity while equipping them for multiple use?…

      When someone reads the words of a psalm as an act of worship, he or she takes over, in a sense, the psalm’s authorship. It may have been written by an ancient Levite, but at the moment of its recitation, its words become the worshipper’s own: they speak on his or her behalf to God…. This seems to me a remarkable phenomenon, precisely because what is crucial are not the words themselves, but the mind of the worshiper who utters them. The very attitude of prayer pushes to the background the historical circumstances of the psalm’s composition. The true author is now the worshipper himself.

–  James L. Kugel, How to Read the Bible: A Guide to Scripture, Then and Now, 471-3.