Halakhah sa Awit ng mga Awit 2:9: Mishneh Torah, Prayer and the Priestly Blessing & Kitzur Shulchan Arukh

How is this rite performed outside the Temple? When the Reader of the congregation reaches the paragraph in the Amidah referring to the restoration of the ancient service and he utters the first word of that blessing beginning "Be pleased",^*The first of the last three blessings of the Amidah. all the priests in the synagogue leave their places, proceed to the platform in front of the ark, stand there, with their faces towards the ark and their backs towards the congregation, their fingers bent in their palms, till the Reader concludes the paragraph of thanksgiving.^*The second of these last three blessings. Then they turn their faces toward the congregation, straighten their fingers, raise their hands to a level with their shoulders and begin reciting, "May the Lord bless thee". The Reader prompts them, word by word, and they repeat, as it is said, "Say unto them", which means that they are to wait till he recites. When they have ended the first verse, all the people respond, "Amen". The Reader of the congregation prompts them in the second verse, word for word, which they repeat till they have ended the second verse, when all the people respond, "Amen". And so with the third verse.

They raise their hands to the level of their shoulders³⁰Maseches Sotah 38a. and stretch them out, and separate their fingers in such a way that there are five spaces between them. That is, between two fingers and two fingers there is one space, and between the two fingers and the thumb, there is another space, and the same with the other hand; making four spaces. And between the two thumbs there is another space, which makes a total of five spaces.³¹Shulchan Aruch 128:12. This must be done, because it is written, "He is peering through the lattices,"³²Shir Hashirim 2:9. five open spaces.³³Rosh, Maseches Megillah 3:21, Midrash. (Tanchuma Parshas Nasso) Metaphorically, Hashem watches over His people through those five spaces between the fingers of the kohanim at the duchan. (Hei Charakim, hei, is the equivalent of the number five, and Charakim means openings) He must be careful that his thumbs should not touch each other, so that there will be five spaces. He must raise his right hand slightly above the left and the right thumb should be above the left thumb. They should spread out their hands in such a way that the palms of their hands are turned toward the ground, and the back of their hands toward Heaven.³⁴If the kohein is too weak to raise his hands properly without resting them on something, he may not duchan. This is essential to fulfilling the mitzvah. See Nodah Biyehudah Responsum 5. He should step outside until the kohanim complete the blessings. (Mishnah Berurah 128:50, Acharonim) Some say if he is tired, it is sufficient to keep the fingers separated when he says the words and may relax his fingers between words (Mishnah Berurah 128:43) and the same applies to raising the hands. (see Ksav Sofer 13, Mishnah Berurah 128:55) The kohein must stand. If he is too weak, and must lean on something, he may not duchan (Panam Meiros, Noda Biyehudah, etc.) unlike the Shvus Yaakov, who says if he is unable to stand, he may lean (or sit).