What do we learn from "Nisa Levavenu El Kapayim [El Kel ba'Shamayim]"?
Ta'anis 8a: One's Tefilah is heard [when he prays alone] only if he puts his Nefesh in his hand (Maharsha - it is with his full heart).
Rashi based on Ta'anis 16a: One must truly lift his heart to Hashem, like one who bathes with clean hands. He casts off all filth - "Modeh v'Ozek Yerucham" (Mishlei 28:13). If one confesses and does not abandon sin, it is like immersing while holding a [dead] Sheretz (it does not help). Rav Sadya Gaon, Ri Kara - "El Kapayim" is like Im Kapayim (we lift our hearts with our hands).
Yevamos 105b: One who prays must face up 1 .
Rashi: [One must lift the heart] to the clouds - "v'Hinei Av Ketanah k'Chaf Ish Olah" (Melachim I, 18:44), "Al Kapayim Kisah Ohr" (Iyov 36:32).
Ibn Ezra #1: We give our hearts for a gift, like "va'Yisa Masa'os" (Bereishis 43:34).
Ibn Ezra #2: He will carry his heart in his hands.
Palgei Mayim: Ma'aseh is called Kapayim; we find this often in Tanach. Levav refers to intent. I.e. we will designate the deed and intent solely for Hashem, and then Hashem will be with us to save us.
105b: Another opinion says to look down (towards the Shechinah in Eretz Yisrael) - "v'Hayu Einai v'Libi Sham Kol ha'Yamim" (Melachim I, 9:3). R. Yosi said, his eyes should be down, and his heart up, to fulfill both verses.
