Sotah, Chapter Seven, Mishnah Six
This mishnah describes how the priestly blessing was performed, both outside of the Temple and in the Temple. The priestly blessing is Numbers 6:24-26. In Israel it is still done every day. Outside of Israel, some synagogues have the blessing on holidays.
Our mishnah discusses differences between how the blessing is done inside the Temple and outside of the Temple.
The mishnah does not address why the priestly blessing must be recited in Hebrew. The Talmud explains that Numbers 6:23 which reads Thus shall you bless implies that the priests must use the exact words written in the Torah.
How was the priestly blessing [pronounced]?
1) In the province (outside of the Temple) it was said as three blessings, but in the
Temple as one blessing.
2) In the Temple the name was uttered as it is written, but in the province in its substituted name.
3) In the province the priests raise their hands at the height of their shoulders, but in the Temple above their heads, except the high priest who does not raise his hands higher than the frontlet (on his forehead).
a) Rabbi Judah says: even the high priest raises his hands higher than the frontlet, as it says, And Aaron lifted up his hands toward the people and blessed them (Leviticus 9:22).
Section one: There are three clauses in the priestly blessing. Outside of the Temple after each clause the people would answer amen. However, inside the Temple, the people didnt respond until all three clauses were recited, and when they did respond they didnt say amen but rather Blessed is the God of Israel forever and ever.
Section two: In the Temple the priests pronounced Gods name as it is written YHWH. (Today we dont know how this word was pronounced). However, outside the Temple it is pronounced using the substitute name Adonai, the way we pronounce Gods name today.
Section three: In the Temple the priests raise their hands above their heads when blessing the people, while outside of the Temple, they raise their hands no higher than their shoulders.
According to the first opinion, the high priest did not lift his hands higher than his head, for on his head was a frontlet upon which was written Gods name (Exodus 28:36). Rabbi Judah believes that just as the rest of the priests raised their hands above their heads, so too did the high priest. Rabbi Judah interprets the blessing mentioned in Leviticus 9:22, a blessing given by Aaron the high priest, to be the priestly blessing in Numbers 6. Just as Aaron lifts his hands above his head, so too do the other priests.