Lifting the Palms
30. The Kohen must bentch the tzibbur with his palms lifted up; this is a feature of the actual mitzva. It is called “lifting the palms” [נשיאת כפים], not “lifting the hands,” implying that the Kohen’s fingertips, which extend from the palm, should also be extended upward somewhat (ברכי יוסף ריש סי' קכ''ח).
Position of the Hands During Birkas Kohanim
31. Shoulder height. The Kohanim lift their hands level with their shoulders (שו''ע סי''ב), as the posuk says (ויקרא ט', כ''ב), “וישא אהרן את ידיו אל העם ויברכם” (מ''ב סקמ''ב). This is essential—if a Kohen does not lift his palms to shoulder height, he does not fulfill his chiyuv (הג' מיימונית הובא בב''י).
32. Right hand higher. The Kohen lifts his right hand slightly higher than his left (שו''ע שם), as that posuk uses the word “ידו,” his hand, in the singular, hinting that one hand should be slightly higher, which presumably means the right hand (מ''ב שם). Even a left-handed person should lift his right hand higher (קונ' איש איטר). However, this halacha of lifting the right hand higher is just l’chatchila; it is not essential b’dieved (שו''ת אבני נזר או''ח סי' ל''א אות י').
33. Palms, or arms too? Some hold it is enough to just raise the palms to shoulder height; the arms may be lower than the shoulders, with the elbows bent (שו''ת אבני נזר שם). Someone who has difficulty lifting the whole length of his arms may certainly rely on this.
34. Some say the whole length of the arms must also be lifted to shoulder height, i.e., the elbows are completely straight, not bent. The reason is because the entire arm is called “יד,” as we find with tefillin, where the posuk says “וקשרתם לאות על ידך,” which refers to the arm. Thus, a Kohan must lift his whole “יד” for Birkas Kohanim, i.e., the arm too (באר שבע סוטה דף ל''ז ע''ב, קרית ספר הל' תפילה פי''ד מצוה י''ט).
35. Hands open, facing down. The fingers must be extended so the hand is open, not closed into a fist. The palm should face down toward the ground, with the back of the hand facing up (שו''ע שם).
36. Separate fingers to make five gaps. The Medrash (תנחומא פ' נשא) says, “He watches from the windows” — from between the Kohanim’s fingers; “He peers from the cracks [ה'חרכים]” (שיר השירים ב', י') — when they stretch out their palms. From here derives the minhag that the Kohen must separate and arrange his fingers in such a way that he creates five gaps, based on the posuk “ה' חרכים.” The Shechina “peers through the spaces” כביכול.
37. Five spaces. It should be noted that there are multiple different minhagim as to how exactly to separate the fingers to create five spaces (ראה בסוף הספר נשיאת כפים כהלכתה בתוספת ברכה סי' ז' באריכות). Each Kohen should follow his family minhag. If a Kohen does not have a particular minhag, he should do the method mentioned by the poskim, as will be explained.
38. Five spaces are created by keeping two fingers touching each other; then another two fingers touching each other, creating one space between the two groups of fingers. Then, the thumb is held apart from the two fingers next to it to create another space. The same is done with the second hand, creating four spaces. Then, the two thumbs are brought together until they are touching (מג''א סקי''ט), creating another space between the two thumbs, for a total of five spaces.
39. Holding the two thumbs together. We find two ways to put the two thumbs together to create a space between them.
40. The first way is to put the two tips of the thumbs together with the bottoms of the thumbs separated, creating a space between them [ג]. In this method, the other spaces are facing outward, whereas this space faces inward, toward the Kohen’s body; see illustration [taken with permission from the sefer נשיאת כפים כהלכתה].
41. A second way is to bend the thumbs and bring them together at the bent point, such that a space is created [ג] facing outward. In this way, it matches up with the other spaces, which also face outward; see illustration [this is what my rebbi, R’ Shamai Kehos HaKohen Gross showed me he does with his hands].
