1.

(a) It is very important that a person should be clean when he prays, and this is why he is required to excuse himself before he starts Davening. The Gemara later (23a) states that if someone knows in advance that he will need to be excused he should not pray, and if he did so his Tefilah is an abomination. This is derived there from the verse, "Prepare to meet your G-d, O Israel" (Amos 4:12).

(b) The Emek Berachah explains further why a hygenic body is important during prayer. In Tehilim (35:10), David ha'Melech exclaims, "All of my bones shall say: Hash-m, who is like you!." This describes the way we pray; we praise Hash-m with our entire being. It follows that our entire body must be pure before we commence our Tefilos.

(c) Another insight tells us why this is necessary specifically for Malchus Shamayim Sheleimah -- for a complete acceptance of the kingship of Hash-m. If one is not excused before the start of the Tefilah it is likely that one will have to interrupt in the middle of the prayers. As a result of these interruptions, one's acceptance of Malchus Shamayim will not be considered complete.

2. In the same way that one should ensure that his body is internally clean before he prays, one should be careful that it is externally clean. For other laws of the Torah we find that one is required to immerse oneself in a Mikvah in order to attain a state of purity. The Chidush of the Gemara is that for prayer, one may be slightly more lenient and it suffices merely to wash one's hands. The Gemara derives this from the verse, "I will wash my hands with cleanliness" (Tehilim 26:6). In fact, the Rambam (Hilchos Tefilah 4:3) writes that before Shacharis in the morning a higher level of cleanliness is required and one should wash one's feet and face in addition to his hands. In contrast, for the other Tefilos of the day, it suffices to wash one's hands, and this is considered just as good as immersion in a Mikvah.

Kol Tuv,

Dovid Bloom