The most important words in any language are those that can’t be easily translated. “Modim,” which begins the 6th blessing of the Shabbat amidah (the 18th blessing of the weekday amidah) is one of those words.
One the one hand, it refers to thanks (as in “todah rabbah”). But it also means “admit,” as in the vidui (confessional) prayer on Yom Kippur.
There is no word in the English language that captures both of these nuances, and so “modim” has to be translated as “gratefully acknowledge.”
The prayer makes reference to both nuances, acknowledging that G-d is our G-d, the G-d of our ancestors, the shield of salvation for every generation; but also thanking G-d for the gift of our lives, our souls, the miracles which we receive every day, and the goodness we experience constantly.
Someone once said that there can be no joy without gratitude. Gratitude is the natural response to receiving a gift, and if there is no gratitude, then there is no consciousness of the gift having been given. This prayer (which, I must admit, is one of my favorites) is intended to help us foster that consciousness.
It is interesting to note that there is another version of the prayer (called “the rabbis’ modim”) that is recited by the congregation in an undertone while the Cantor is repeating the amidah. It is the only prayer for which we have such a private meditation, an indication of the centrality of “grateful acknowledgement” in the worldview of the rabbis.
Gratitude turns what we have into enough—which is an especially important message on Shabbat, but something we ought to remember all week long.