A person’s deepest desire is to draw close to God and to thank Him for all His goodness. But since God is so exalted and mighty, great and awesome, one becomes overwhelmed and awestruck when confronting His tremendous grandeur. He naturally bows and prostrates himself in self-negation before God. As we have seen, there are three types of bowing. Each has its own significance.
Prostration (hishtaḥavaya) means lying prone with one’s hands and feet extended, expressing absolute self-effacement before God. This is not a self-effacement of non-existence, but a self-effacement born of clinging to God, through which one can draw down blessing upon himself from the Source of life. King David frequently bowed to God, thanking Him for His help, as we read, “But I, through Your abundant kindness, enter Your house; I bow down in awe at Your holy Temple” (Tehilim 5:8). And similarly, “I bow toward Your holy Temple and praise Your name for Your kindness and faithfulness, because You have exalted Your name, Your word, above all. When I called, You answered me, You inspired me with courage…. High though the Lord is, He sees the lowly…” (ibid. 138:2-8).
When performing kida, one remains standing but bends his head to the ground, indicating profound submission. Even though he remains standing, he is bent double in total submission.
Keri’a involves falling to one’s knees and bending forward so his face is on the ground. It is a combination of prostration and kida, of self-effacement and submission. As in prostration, one’s entire body is near the ground; like in kida, one bends in submission to his Creator.
The Sages tell us that good things happen as a result of prostration:
Avraham returned unharmed from Mount Moriah together with Yitzḥak only in the merit of his prostration, as we read, “We will worship (ve-nishtaḥaveh) and we will return to you” (Bereishit 22:5). Israel was redeemed from slavery only in the merit of their prostration, as we read, “When they heard that the Lord had taken note of the Israelites and that He had seen their plight, they bowed low in homage (ya-yikdu va-yishtaḥavu)” (Shemot 4:31). The Torah was given only in the merit of prostration, as we read, “Then He said to Moshe, ‘Come up to the Lord, with Aharon, Nadav and Avihu, and seventy elders of Israel, and bow low from afar’” (ibid. 24:1). Ḥanna was remembered only in the merit of prostration, as we read, “And they bowed low there before the Lord” (1 Shmuel 1:28). Only in the merit of prostration will the exiles will be gathered in, as we read, “And on that day, a great ram’s horn shall be sounded; and the strayed who are in the land of Assyria and the expelled who are in the land of Egypt shall come and worship (ve-hishtaḥavu) the Lord on the holy mount in Jerusalem” (Yeshayahu 27:13). The Temple will be rebuilt only in the merit of prostration, as we read, “Exalt the Lord our God and bow down to His footstool; He is holy!” (Tehilim 99:5). The dead will be brought back to life only in the merit of prostration, as we read, “Come, let us bow down and kneel (nishtaḥaveh ve-nikhra’a), bend the knee before the Lord our Maker” (ibid. 95:6). (Bereishit Rabba 56:6)
All who entered the Temple courtyard would prostrate themselves before God. (See m. Midot 2:3.) When the daily offering was brought and Levi’im sang and blew the trumpets, the people standing in the courtyard prostrated themselves (m. Tamid 7:3).
When a person repents and confesses before God, it is proper that he prostrate himself, following the example of Moshe who prostrated himself when he prayed to God to forgive Israel’s sins (Bamidbar 14:5, 16:22; Devarim 9:25). For this reason, the Jews standing in the courtyard would prostrate themselves when the Kohen Gadol uttered the Tetragrammaton during the Yom Kippur confessions (Yoma 66a).
Following this line of thought, the Sages ordained that people bow five times during every Amida. This bowing is done while standing but bending deeply at the waist – similar to kida (Peninei Halakha: Prayer 17:6). It was also customary to prostrate oneself after the Amida, while confessing and offering supplications to God. This became known as Nefilat Apayim (“falling on the face”) and was a precursor to today’s Taḥanun (MT, Laws of Prayer 5:1, 13-14; Tur OḤ 131; Peninei Halakha: Prayer 21:1).
However, several concerns led to the discontinuation of the custom of actually “falling on the face.” On the halakhic level, besides the problem of prostration on a stone floor, there is an additional concern as well. A prominent person is permitted to “fall on the face” only when he is certain that God will respond, as He did to Yehoshua bin Nun (Megilla 22b; SA 131:8), and who can be certain of this? However, the primary concern is based on Zohar. It speaks extensively about the power of Nefilat Apayim, during which the supplicant must truly devote himself to God and see himself as if he is dead. It continues:
This must be done with intense concentration; then God is merciful and forgives his sins. Fortunate is the person who knows how to appeal to and worship his Master willingly and intentionally. Woe is to one who tries to appeal to his Master when his heart is distant and unwilling. He is the subject of the verse, “Yet they deceived Him with their speech, lied to Him with their words; their hearts were inconstant toward Him” (Tehilim 78:36-37). If the person says, “O Lord, I set my hope on You” (ibid. 25:1) while his heart is distant, this will be responsible for his premature death. (Zohar, Bamidbar 121a)
Since we are concerned about not being fully focused when we petition God, and about not being deserving, we no longer prostrate ourselves during Taḥanun. Instead, Ashkenazim and some Sephardim sit, leaning forward and resting the forehead on the forearm. Other Sephardim avoid even that (Peninei Halakha: Prayer 21:3).
However, on Yom Kippur, thanks to the sanctity of the day and our intense devotion, we are not concerned about any of this. Therefore, the custom is to bow during the description of the avoda, as is appropriate for a penitent.