Sha'ar HaKavanot

First drush:

Now let us explain the general principles that lie in the order of the arrangement of the morning prayer. Know that from the beginning of the prayer until Barukh she-amar is the world of Asiyah; from Barukh she-amar until Yotzer or is the world of Yetzirah; from Yotzer or until the end of the blessing of the Patriarchs is the world of Beriah; and all the rest of the Amidah is the world of Atzilut. The order of Asiyah proceeds from below upward. And in order to unite Asiyah with Yetzirah — and behold, there are harsh and powerful kelipot in it — one must therefore first unite the head of Yetzirah with the head of Asiyah, and only afterward the remainder of Yetzirah, which proceeds from below upward; and so too Beriah proceeds from below upward. The blessing of the Patriarchs is the head of Beriah, called the Holy of Holies chamber of Beriah, up to the end of “Blessed are You, HaShem, Shield of Abraham,” and all the rest of the Amidah is in Atzilut. And this is the explanation of all the foregoing: for the eighteen blessings from al netilat yadayim until the blessing over Torah are the eighteen blessings of the Yesod of Asiyah; and from Hodu until Barukh she-amar is the head of Asiyah, its Holy of Holies chamber; and Barukh she-amar is the Holy of Holies chamber, the head of Yetzirah — and therefore it contains thirteen occurrences of barukh, the numerical value of eḥad, and this is the secret of the thirteen measures of mercy that are in the world of Yetzirah. And therefore Barukh she-amar has eighty-seven words, according to the version we shall copy below, God willing, to hint that it is the head of Yetzirah, of which it is said “his head is finest gold (paz פ”ז, gm. 87)”; and therefore one must say ha-mehullal be-feh בפה amo — which comes to בפ”ה 87 in gematria — and not be-fi amo as it is written in the maḥzorim. And afterward come the eighteen Names contained in those verses from Yehi khevod HaShem le-olam until Tehillah le-David, as is known; and these are the eighteen blessings of the Yesod of Yetzirah. And since it is known that in each world of the four worlds ABiYA there are all ten sefirot and all the partzufim — namely Arikh Anpin, Abba and Imma, and Za and Nukva — therefore at the end of Yetzirah we again mention eighteen Names of Havayah in the Song at the Sea, and the thirteen praises of Yishtabaḥ, which are “song and praise, hallel and hymn,” etc.