Halakhah su Ezechiele 3:78

And about the reason that water purifies everything impure, I would think on the side of the simple understanding that it is in order that a man see himself with the immersion as if he is created at that time, [just] like the whole world was water before man was upon it - as it is written (Genesis 1:2), "and the spirit of God floated upon the face of the waters." And through this comparison, he place upon his heart that [just] like he is renewed in his body, he also renew his actions for the good, fix his actions and be exacting in the way of God, blessed be He. And therefore the Sages said that the purification is not fit with water that is in a vessel, but rather only with living water - or collected [water], which is on the ground and, in any case, not in a vessel - in order to place in his heart the thought as if the world was entirely water, and [that] he is renewed with his emerging from them, as we said. But if the water was in a vessel - or even if it passed through a vessel - this matter that we said would not be set in the thought of the one immersing. As there is a limit to all that is in a vessel, which is the creation of the hands of man. And therefore when he immerses in a vessel, he will not think as if the whole world is water like at the beginning [of Creation], and that he is renewed at that time. 'And the one who accepts, will accept; and the one who refrains will refrain.'

The fiftieth day of the count of the Omer is the holiday of Shavuot. The prayer service is like the holiday of Passover, rather we say "the Holiday of Shavuot, the time of the giving of our Torah". We say full Hallel. We take out two Torah scrolls and read in the first one of five [sections] from "The third month" until the end of the order. The Maftir is read in the second scroll, "On the day of the first fruits". As Haftorah we read the chariot of Ezekiel, and end with the verse "and the wind took me up."

He says “כתר²¹³The Keter, כתר, was an ancient beginning of the Kedushah, קדושה, or sanctification prayer. It is no longer said and Kedushah now begins with the word na'ariẓkha, נעריצך. It is part of the Sabbath and festival Musaf Service (see footnote 166).
The Kedushah said during the Musaf Amidah is different than the Sanctification recited in the Shaḥarit Amidah on the Sabbath (see footnote 17). The Musaf Sanctification dwells more sublimely on the majestic conception of the angels in heaven glorifying the Eternal King and it introduces Israel proclaiming in response to the angelic choir, the holiness, glory, unity, and sovereignity of God's name. The Shema, the congregation's confession of faith, is part of the Musaf Kedushah (see footnote 17, section (3)).
The Shema entered the Musaf Kedushah as the result of a sixth century persecution. The Byzantine Empire forbid Jews to recite the Shema in public worship. On Sabbaths and festivals government spies would enter the synagogues to make sure the Shema was not said in its regular place during the Shaḥarit Service. As a means of getting the Shema into public prayer, the reader would insert it into the Musaf Kedushah, a place where the spies would not expect it and thus not be aware of it. The Shema has remained a part of this Sanctification ever since.
The Kedushah is part of the third blessing of the Amidah and in the Musaf Service for the Sabbath it is made up of the following parts along with connecting sentences: Isaiah 6:3, Ezekiel 3:12, the Shema, Deuteronomy 6:5, and Psalms 146:10. On festivals there is an additional verse from Zechariah 14:9 following the Shema.
Hertz, op. cit., pp. 528-31; 816-19.”, “the crown”, just as in the Additional Service.²¹⁴Musaf, מוסף; see footnote 166.