Halakhah zu Jechezkiel 1:7

One must put her legs together so that they look like one leg. The reason for this is that the separation of one’s legs exposes one’s material side and represents the pursuit of worldly matters. Thus, we keep our feet together in prayer just like the kohanim who, in their ascent of the altar, would walk heel-to-toe to avoid spreading their legs. Furthermore, putting one’s legs together symbolizes the annulling of the powers in one’s legs, demonstrating that we have but one desire, to stand before Him in prayer. The Sages learn this from the angels, of whom it is said: “Their legs are a straight leg” (Yeḥezekel 1:7), meaning that their legs were placed so close together that they appeared as one leg (Berakhot 10b; y. Berakhot 1:1; see Maharal, Netiv Ha-avoda §6).

Your feet should be placed next to each other as if they were only one, to resemble the angels, of whom it is said: ''And their feet were straight feet."¹³Ezekiel 1:7. In Hebrew, regel means one foot. Which means their feet [ragleihem] appeared as one foot [regel]. Your head should be bent slightly, and your eyes closed, so as not to gaze at anything. If you are praying from a Siddur¹⁴I.e. a prayer book. do not remove your eyes from the Siddur. Your hands should be upon your heart, the right hand upon the left. You should pray wholeheartedly with fear, reverence and humility, as a poor man standing at the door;¹⁵In the manner of a beggar pleading for alms. and pronounce the words with concentration and exactness. Everyone should pray according to his [accustomed] form [of prayer], whether it be Ashkenazic or Sefardic,¹⁶There are various texts of the Siddur prayers. or another, [for] they are all based on sacred origin. However do not intermingle words from one form with another, because the words of each form are numbered and counted, based on important mystical concepts, and nothing should be added or subtracted from them.¹⁷One should follow the text of the Siddur he is using.

The Position of One's Limbs at the Time of Prayer, containing 4 s'ifim
One should position one's feet next to each other as though they are one, in order to imitate angels, as it written regarding them: “their feet were a straight foot” [(Ezekiel 1:7)], which is to say their feet appeared as one foot. (Some say when one stands to pray one should take three steps forward in the way of coming close and approaching a matter that must be done.) (Rokeach)