During Pesukei d’Zimrah and Birkot Keriat Shema a person is permitted to either sit or stand, but once he reaches Shemoneh Esrei (the Amidah), he must stand with his feet together. When one stands, he summons his complete being, from head to toe, to prayer. In addition, his standing expresses his awe and fear toward the King of the world. Therefore, one must not lean against anything while reciting the Amidah, for anyone who is supported by something even slightly is not considered to be in a state of fear. In extenuating circumstances, for instance, when someone is weak and must lean against something, he should try to lean only slightly, such that if the support should be taken from him, he would remain standing on his own. In that way, although he is not standing in fear, he is at least considered to be praying in a standing position (Shulchan Aruch 94:8; Mishnah Berurah 22).
One must put his legs together so that they look like one. The reason for this is that the separation of one’s legs exposes the material side of a person and represents the pursuit of worldly matters. Thus, we keep our feet together in prayer just like the Kohanim who, in their ascent to 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. Chazal learn this from the angels, of which it is said (Ezekiel 1:7), “Their legs are a straight leg,” meaning, their legs were placed together so that they appeared to be one leg (Berachot 10b; Yerushalmi, chapter 1, halachah 1; and see Maharal Netiv Ha’Avodah 6).
One must put the entire length of his foot next to the other so that they will seem as much as possible as one leg, unlike those who just put their heels together (Shulchan Aruch 95:1; Talmidei Rabbeinu Yonah). However, b’dieved, if one prayed with his feet apart, he still fulfilled his obligation (Mishnah Berurah 1; Kaf HaChaim 2).
A person who is ill and cannot stand may recite the Amidah while sitting. If he is unable to sit, he may pray while lying down. However, according to a number of poskim, if before the time to pray lapses he has gathered strength and is able to stand, he will need to repeat his prayer while standing, since the essence of the mitzvah of the Amidah is in a standing position (Shulchan Aruch 94:9). Nevertheless, in practice, the Acharonim agree that whether he prayed sitting or standing, he fulfilled his obligation b’dieved and even if he is able to stand later, he is not required to repeat his prayer while standing (Mishnah Berurah 94:27; Kaf HaChaim 34).
Even one who must recite the Amidah while sitting or lying down should try to put his feet together and bow his head at the appropriate places. When a person sitting in a wheelchair finishes his prayer, he should wheel himself slightly backwards, approximately the distance of the three steps with which a healthy person departs from prayer (see further in this chapter, halachah 16).