Spirit of the Law: Rosh Hashanah II

Kitzur Shulchan Aruch, chapter 129:2 “On Rosh Hashanah and Yom Kippur, during Shemoneh Esrei (the silent prayer), there are those who remain bent over in a bowing position from beginning to end.
Although they are stooped the entire time, they must nevertheless stand erect before and after the four points in the tefillah where one is obligated to bow. This serves to distinguish between bowing which is obligatory and that which is not.”

Reb Nosson explains that when we bow at the four points of our obligation, we transform our spiritual descents into ascents. The act of bowing physically comprises first a fall, followed by a conscious recouping of stature.
In prayer, we accomplish this by subduing our egos and admitting that we need help—by prostrating ourselves physically and spiritually before Hashem. After the fall, Hashem helps us to rise up once again.
The places in the Shemoneh Esrei where we bow are seminal points in the tefillah; we are instructed to bow at precisely these moments so that we can receive the supernal illuminations sent down by Hashem at exactly those points in the prayer.
One who fulfills his duty and bows with the express purpose of transforming his “falls” into ascents merits a new level of spiritual awareness, the direct result of the spiritual light he receives at those times.
Why do we bow? To demonstrate that we are willing to go to any lengths to become more fulfilled human beings with a true spiritual connection to Hashem and His will. We do it even if this demands the ultimate nullification of our selves—manifest by bowing down before Him.
It is now clear why a sharp distinction must be made between the four obligatory bows, and any optional bowing.