Psalm 151 is an additional Psalm found in the Septuagint (LXX) but which is absent from the Masoretic text, though a copy of the text of the Psalm in Hebrew has been discovered at Qumran among the Dead Sea Scrolls.
Date and authorship
The Psalm was apparently composed at some point after the book of Psalms was essentially settled but before the Greek text (LXX) was finalized. Its presence among the Dead Sea Scrolls suggests that while it was left out of the Masoretic textual tradition it was, in fact, part of the Hebrew tradition before the appearance of the Greek tradition. Accordingly, we can safely suggest that the Psalm originated sometime before the 2nd century BCE. Its author is unknown. Nonetheless he was a person thoroughly familiar with the textual tradition of the biblical books of 1 and 2 Samuel and adopted its reading of the David story without alteration.
The Psalm is a straightforward reading of the victory of David over the Philistine Goliath (although Goliath is never mentioned within the text of the Psalm).
DeSilva, David. Introducing the Apocrypha: Message, Context and Significance. Grand Rapids, MI: Baker Books, 2002.
Flint, Peter W. The Dead Sea Psalms Scrolls and the Book of Psalms. Leiden: Brill, 1997.
Harrington, Daniel. “Psalm 151.” In Harper’s Bible Commentary. Edited by James L. Mays. San Francisco: Harper & Row, 1988.
Charlesworth, J. H., and J. A. Sanders. “Psalm 151.” Pages 612-15 in vol. 2 of The Old Testament Pseudepigrapha. 2 vols. New York: Doubleday, 1985.
Sanders, J. A. The Dead Sea Psalms Scroll. Ithaca. New York: Cornell University Press, 1967.
Sanders, J. A. The Psalms Scroll of Qumran Cave 11 (11Qpsa). Discoveries in the Judean Desert IV. Oxford: Clarendon, 1965.