The application of literary theory to sacred literature, while running the risk of diminishing the elevated stature of sacred texts, also carries the potential to deepen our appreciation for these sources. The upside to bringing literary methodologies to bear is especially evident in regard to piyyutim, religious poetry. In connection with the present holiday of Pesach, one particularly shining example is the ever-popular Dayenu.
Had this been a comprehensive study of the classic song, we would explore its historical roots in depth, including Yisrael Yuval's stimulating thesis that Dayenu ought best be viewed as a polemical retort to Melito of Sardis' scathing anti-semitic Easter homily (Two Nations in Your Womb, pgs. 70-71). For our purposes, however, it suffices to note, with Yuval, that while scholars have long assumed that Dayenu was composed in the early centuries of the common era, in fact the earliest appearance of the zemer in Hagadot is in the tenth century, in the Hagadah of Rav Saadiah Gaon. The song's author remains unknown.
As to content, the song's basic thrust is fairly evident. Fifteen times in a row, we declare our indebtedness to God for His miracles, beginning with the Ten Plagues and running through the Jews' entry to the land of Israel and construction of the Temple. The song is preceded by an introductory line emphasizing just how many acts of kindness God has performed for the Jewish people, and is followed by a extended litany of items that are worthy of thanksgiving, all drawn directly from the song. As many have observed, Dayenu's basic premise eludes obvious explanation: why would we thank God, for instance, had He split the sea but not drowned the Egyptians? Or if He had brought us to Sinai without giving us the Torah? Or for sinking the Egyptians in the sea but having failed to provide for our basic existential needs in the desert? We will return to this basic problem at the end of our study.
Regarding structure, the poetic patterns are highly repetitious and therefore fairly easy to discern. Each stanza asserts "had He done "x" for us but not done "y" for us, it would have been sufficient." Thus, the word "ilu" begins the first line of each stanza, and "ve-lo" opens the second line of all the stanzas. The second line of each preceding stanza repeats as the first line of the following stanza, amplifying the repetitiveness. "Dayenu" concludes every stanza; in poetic terminology, this repetition of the same term at the end of each stanza is called an epistrophe. Additionally, in many Hagadot, Dayenu is set off to the left side of the page, granting it greater prominence and highlighting its constant recurrence.
What is more, the song's frame further underscores the redundancy motif: Dayenu opens with the declaration, "How many levels of favors has the Omnipresent bestowed upon us," and concludes with the paean "How much more so should we be grateful to the Omnipresent One for the doubled and redoubled goodness that He has bestowed upon us." That's a lot of doubling.
What is more, the "doubling" theme is manifest not only in the song's skeletal structure but also in its content. For one, many of the specific instances of thanksgiving seem to overlap significantly with others, to the point that it is not obvious how the paytan avoids the charge of redundancy. For instance, we thank God for having wrought plagues upon the Egyptians, their gods and their firstborns. We recognize Him for splitting the sea, taking us through and capsizing our enemies. Drawing a subtle distinction, we thank God for having provided for both our general needs and the manna in particular while we journeyed in the desert. We then single out both the experience of having stood before Sinai and having received the Torah. While it is possible to account for the subtle differences between each of these phenomena - and numerous commentaries do precisely that  - the sense one gets is that the recapitulations are intentional. After all, as a glance at the Exodus narratives makes plain, it is immediately obvious that the paytan could have easily chosen any number of other examples that would have avoided the charge of redundancy. Instead, it appears that the reiterations of Dayenu are intentional, even essential to the song's structure and conceptual matrix.
In this vein, it is worth pointing to the common tune to which Dayenu is sung, in which the word Dayenu repeats numerous times in each stanza. I would argue that this particular harmony is consistent with the epistrophe and overall structure of the song, which keep returning us to the refrain of Dayenu.
Interestingly, Joseph Tabory (The JPS Commentary on the Haggadah, pg. 97) theorizes that Dayenu was initially a refrain, so that one person would read each stanza, and a choir would respond "Dayenu" upon each segment's conclusion. This format, familiar to us from Hallel and many piyyutim recited during the High Holidays, reinforces the notion that the repetition of Dayenu is the song's focal point. In Tabory's striking formulation, which sums up everything we have seen so far, "at times the content itself is subjugated to the form."
Another manner in which the content is subjugated to the form concerns the piyyut's numerology, in particular its implicit emphasis on the number fifteen. As pointed out by many scholars in their Hagadah commentaries (Ritva, Abudarham, Hagadah Sheleima), fifteen carries numerous allusions in the Jewish tradition: the fifteen steps in the Temple courtyard; fifteen corresponding Songs of Ascent (Shir Ha-Ma'alot) in Psalms (chapters 120-134), which were sung by the Levites on those fifteen steps; fifteen blessings recited each morning; and fifteen terms used to praise God in "Emet Ve-yatziv," the praise immediately following the Amidah. Additionally, as Ritva emphasizes, fifteen is the mathematical sum of י-ה, one of God's names.
Of course, some of these specific correspondences might be significant. For example, the importance of the number fifteen to the Temple parallels the piyyut's final stanza, in which we thank God for the Temple. But the broader point is the key one to make: the fifteen-fold repetition again turns our attention away from the particular details of the thanksgiving to the larger motif of repetition as a dominant theme in its own right.
What, then, are we to make of all this repetition, which is shot through nearly every element of Dayenu? The key would seem to be the clusters of seemingly redundant categories of praise we mentioned earlier: the plagues, the splitting of the sea, provisions for the Jews in the desert, and the Revelation at Sinai. It is obvious that each of these experiences is deserving of praise; what is less evident is that each of these stages, as all others, in the redemption can best be appreciated from multiple perspectives. Much as one must turn an exquisite diamond 360 degrees to fully appreciate its beauty, so too with the Exodus. Only by taking each of its central events and considering them from almost every conceivable angle can we begun to appreciate the extent of the gratitude we owe God.
It is worth adding that the passage in the Hagadah immediately preceding Dayenu might lend support to our interpretation. Immediately after affirming that there were ten plagues in Egypt, the Hagadah cites a three-way dispute between Rabbi Yose Ha-Glili, Rabbi Eliezer and Rabbi Akiva as to the number of makkot performed by God in Egypt at the Yam Suf respectively: 10 and 50, 40 and 100, or 50 and 250. How we are to understand the positions of Rabbi Eliezer and Rabbi Akiva? Do they completely deny the traditional notion of ten plagues? This seems implausible: For one, the Hagadah had just cited the existence of ten plagues – without dissent. What is more, the Torah itself clearly differentiates among the ten plagues; clearly, the rabbis do not reject the Torah itself! Instead, it seems apparent that none of the sages disputes the basic count of ten. Instead, they are suggesting that, in the spirit of Dayenu, when we more closely consider the ten plagues (according to Rabbis Eliezer and Akiva) and the splitting of the sea (according to everyone) we unearth additional layers of makkot that we might not have immediately appreciated. Each of these additional dimensions is considered another plague in its own right.
This interpretation enables us to resolve the question we posed at the outset. Dayenu does not intend to assert that, for instance, we would have been grateful if God had split the sea but drowned us along with the Egyptians. Instead, its message is that each stage is remarkable in its own right and worthy of close, comprehensive analysis and appreciation.
A careful study of Dayenu's literary qualities, then, enables its central theme to emerge with shining clarity. In expressing our appreciation for the Exodus - and, presumably, for all the kindnesses we merit - it is not enough to see the larger picture from 10,000 feet. Only by engaging in close study of all the facets of our experiences, and consequently expressing appreciation to our Benefactor for each and every element thereof, may we be satisfied that we have, in the words of our song, done enough.
 Some commentators took extremes measures in seeking to account for the repetitiveness of these stanzas. Peirush Kadmon, an anonymous medieval commentator cited by the Torat Hayim Hagadah, goes so far as to suggest that the entire song is a series of praises within praises. In other words, the song begins with the broadest appreciation - for the plagues generally - and then continues to limn various aspects of that thanksgiving, analyzing increasingly narrow aspects of that initial wider category of "plagues." In his commentary to the Hagadah, R. Shimon ben Zemach Duran proposes a modified version of this, arguing that Dayenu is best understood as a series of couplet praises, in which two praises are presented at a time.
In Imrei Shefer, Netziv accounts for the unusual choice of praises by pointing to the name of God, HaMakom, literally The Place, which brackets Dayenu. Netziv explains that HaMakom denotes God's hashgaha, active concern for and intervention in earthly affairs. Thus, each element mentioned in the song was not essential to the Exodus, but instead was about something extra God performed in order to demonstrate His concern for the Jewish people. For example, "judgments" refer to additional plagues that God brought in order to demonstrate his active involvement in human affairs. Netziv's interpretation, however, also seems difficult, since many of the details included in the song do seem to have been essential, such as the Plagues, splitting of the sea and giving of the Torah.
While each of these particular interpretations is beset by a number of obvious difficulties, it is evident that all three commentators were inspired by the intentional doubling that Dayenu manifests.