Say to Aaron and his sons: Thus shall you bless the children of Israel, and you shall say to them:

“אמור is infinitive. Similar forms are זכור (Exodus 20:8), שמור (Deuteronomy 5:12); in O. F. disant, (English = saying). אמור להם SAYING UNTO THEM — so that all of them should hear the blessing (it would not suffice to pronounce the blessings upon the Israelites in their absence; cf. Sifrei Bamidbar 39). אמור is written plene (with ו after the מ) thus indicating: ye shall not bless them hurriedly and hastily, but devoutly and with a whole heart (Midrash Tanchuma, Nasso 10).”

“SPEAK UNTO AARON AND UNTO HIS SONS, SAYING: THUS YE SHALL BLESS. I have already mentioned in Seder Vayehi Bayom Ha’shemini, 22. that He commanded Aaron to lift up his hands towards the people and bless them on that day [i.e., the eighth day of the initiation of the priests, which was the day of the final erection of the Tabernacle], and here He commanded Aaron and his sons to do so throughout the generations, and He explained what the blessing was with which they are to bless them. He mentioned this blessing in connection with the setting up of the Tabernacle [discussed in the next chapter], for there the Eternal commanded the blessing, even life forever, just as our Rabbis have said: “In the Sanctuary [the priests pronounced the blessing] using the Divine Name [i.e., the Tetragrammaton], but in the provinces by a substitute Name. In the Sanctuary they pronounced it as a single blessing, but in the provinces [it was pronounced] as three blessings” [the people responding “Amen” to each of the three verses which comprise the priestly blessing], for the blessing in the Sanctuary was singled out by being pronounced with the Proper Name of G-d [i.e., the Tetragrammaton].”

“The Lord bless thee,.... Jehovah, Father, Son, and Spirit; the word "Jehovah" being three times used, and a different accent put to each word, denoting three distinct persons and one Jehovah, according to Deu 6:4; who are each of them concerned in the blessing of the Lord's people, the spiritual Israel of God; Jehovah the Father blesses with all spiritual blessings, with electing, adopting, justifying, and pardoning grace, with regenerating and calling, and persevering grace, and with eternal life: Jehovah the Son blesses particularly with redeeming grace, and has a concern in all the other blessings; the saints are blessed with them in him, they are all in his hands, they are procured by him, come through him, and are the gifts of his grace: and Jehovah the Spirit blesses as a spirit of regeneration and sanctification, as the spirit of faith, as a comforter, as the spirit of adoption, and as the earnest and sealer of the saints unto the day of redemption: and keep thee; from, the evil of the world, from the evil one Satan, from the evil of sin, and the power, prevalence, and dominion of it, and from falling totally and finally by it, and keep in a state of grace unto everlasting salvation.”

“THE FORM OF BLESSING THE PEOPLE. (Num 6:23-27) Speak unto Aaron and unto his sons, saying, On this wise ye shall bless the congregation of Israel, &c.--This passage records the solemn benediction which God appointed for dismissing the people at the close of the daily service. The repetition of the name "Lord" or "Jehovah" three times, expresses the great mystery of the Godhead--three persons, and yet one God. The expressions in the separate clauses correspond to the respective offices of the Father, to "bless and keep us"; of the Son, to be "gracious to us"; and of the Holy Ghost, to "give us peace." And because the benediction, though pronounced by the lips of a fellow man, derived its virtue, not from the priest but from God, the encouraging assurance was added, "I the Lord will bless them." Next: Numbers Chapter 7”