הלכה על ברכות 20:28

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).