The penultimate blessing of all ‘Amidot (standing devotions) is the Thanksgiving Blessing, which begins with the words Modim ana’hnu Lakh (“we thank You/we acknowledge Your grace”). However beautiful and central the notion of thanksgiving is to prayer in general and to the ‘Amida in particular, it is by no means easy to parse this text, as it is a written in a rather typical rabbinic style of liturgical poetry which non-initiates do not directly recognize.
A careful study of the text will, however, make some of that poetic beauty stand out and make the text more readily understandable. (Given the subject matter, familiarity with Hebrew is expected.)
The first paragraph of the Modim blessing reads as follows:
מודים אנחנו לך שאתה הוא ה’ א־להינו וא־להי אבותינו לעולם ועד צור חיינו מגן ישענו אתה הוא לדור ודור נודה לך ונספר תהילתך על חיינו המסורים בידך ועל נשמותינו הפקודות לך ועל ניסיך שבכל יום עמנו ועל נפלאותיך שבכל עת ערב ובקר וצהרים הטוב כי לא חלו רחמיך והמרחם כי לא תמו חסדיך מעולם קוינו לך .
The last thirteen words, starting with הטוב clearly for a separate sentence, as I can see no sane way to read them in one breath with the preceding text. Whereas it is preceded by a small litany of things we are thankful for, these last thirteen words are praises of G”d Himself, rather than acknowledgements for His deeds.
The text before הטוב, however, is more difficult to parse. On the one hand, we clearly have two sentences, the first being a statement of intent (“We gratefully thank You” / Modim ana’hnu Lakh) and the second being a litany of things we are thankful for (“we thank You … for our lives that are in Your hand, for our souls which are entrusted to You, etc.”).
However, on the other hand, it is not easy to tell where the first sentence ends and the second begins. Do we read מגן ישענו אתה הוא לדור ודור as a phrase (“You are the shield of our salvation in each and every generation”), as some siddurim have it, with the second sentence beginning with נודה לך ונספר תהלתך (“We thank You and recount Your praise on account of etc.”)? Or do we end the first sentence with מגן ישענו אתה הוא (“You are the shield of our salvation”) and the words לדור ודור are actually the beginning of the next sentence (In each and every generation we thank You … on account of our lives etc.”), as some other siddurim have it?
I used to argue for the second model, as I found the appearance of לדור ודור at the end of a sentence rather awkward, and thought that צור חיינו and מגן ישענו, being parallel, could not tolerate לדור ודור in the phrase, as that would make מגן ישענו אתה הוא לדור ודור three times longer than the clause צור חיינו which it purported to parallel. However, I now believe I was wrong, and that I was in fact led astray by overly zealous punctuation gratuitously breaking up the sentence in too small units.
While it is correct that צור חיינו and מגן ישענו are parallel clauses, that observation obstructs the larger parallelism, namely the two parts of the first sentence. The first leg of that first sentence is מודים אנחנו לך שאתה הוא ה’ א־להינו וא־להי אבותינו. Hence, it is perfectly natural for the second leg to also include שאתה הוא or אתה הוא and a designation of time, i.e. לדור ודור paralleling לעולם ועד. Thus, the second leg is צור חיינו מגן ישענו אתה הוא לדור ודור, without much pausing between צור חיינו and מגן ישענו. (Many siddurim, however, introduce a comma between those clauses, without indicating that the break between לעולם ועד and צור ישענו is more substantial than between צור חיינו and מגן ישענו.) Note how each leg has almost the same number of words, nine, resp. eight.
Hence I want to suggest that chazanim and ba’alei tefilla adjust their rhythm and melody to emphasize this poetic structure, and that they hardly pause between צור חיינו and מגן ישענו.
Another, lesser difficulty presents itself in parsing the second sentence. The astute reader will have noticed that the litany of things we are thankful for is a subordinate sentence that interrupts the flow of the main clause. his is best displayed graphically:
נודה לך ונספר תהלתך
על חיינו המסורים בידך ועל נשמותינו הפקודות לך ועל ניסיך שבכל יום עמנו ועל נפלאותיך שבכל עת
ערב ובקר וצהרים
The phrase ערב ובקר וצהרים (“in the evening, morning and afternoon”) does not modify ועל נפלאותיך שבכל עת, as the נפלאות, the hidden miracles, are said to happen constantly, בכל עת. Instead, the last phrase modifies the first phrase of the sentence, which comes before the litany, forming the coherent sentence “We thank You and shall recount Your praises … in the evening, morning and afternoon,” i.e. at the ma’ariv, sha’harit and min’ha services, in that order, as in Judaism the new day begins with nightfall. That sentence is poetically broken into two by the litany, which lists four things for which we are thankful. These four things are themselves two sets of two (our lives and our souls, and the nissim miracles and the niflaot wonders).