Referring both to God and to man. When God blesses, he bestows that efficacy which renders his blessing effectual. His blessings are either temporal or spiritual, bodily or mental; but in every thing they really convey the good which they import, Nu 6:23-27. The blessings of men to other men, unless they be inspired prophecies, as in Ge 32:32; De 33:1; 1-29, are only good wishes, personal or official, and as it were a peculiar kind of prayer to the Author of all good for the welfare of the subject of them. Blessing, on the part of man towards God, is an act of thanks-giving for his mercies, Ps 103:1; or rather, for that special mercy which at the time occasions the act of blessing: as for food, for which thanks are rendered to God, or for any other good, Ps 116:13; 1Co 10:16.
The less is blessed of the better (Heb 7:7). Aaron and the priests pronounced the benediction (Nu 6:22-27; De 10:8). Jacob and Moses gave dying blessings prophetical of the character and history of the several tribes (Genesis 49; Deuteronomy 33). The cup in the Lord's supper is called "the cup of blessing" from the Passover cup of wine called so because "blessing" was offered over it to God. 1Co 10:15.
Paul says, "the cup which WE bless," namely, the minister and the congregation; not he alone by any priestly authority, but as representing the congregation who virtually through Him bless the cup. The celebrant is the church. The minister is the leader of the congregation. The consecration is the corporate act of the whole church. The joint blessing by him and them (not the cup itself, which in the Greek is not nominative but accusative) and the consequent drinking together constitute the "communion," i.e. joint participation of the blood of Christ.
There are two distinct applications of the word 'blessing.' God blesses His people, and His people bless God, the same word being constantly used for both. It is obvious therefore that it must be understood in more senses than one. Again, we read that "the less or inferior is blessed of the better," Heb 7:7; and though this refers to Melchisedec blessing Abraham, the same thing is true respecting God and His creatures: in bestowing favours God is the only one who can bless. The Christian can say, God hath blessed us with all spiritual blessings in the heavenlies in Christ," Eph 1:3; but the same verse says, "Blessed be the God and Father of our Lord Jesus Christ," meaning "Thanks be to the God and Father of our Lord Jesus Christ." This signification is further made clear by the records of the institution of the Lord's supper. In Matthew and Mark the Lord took bread, and 'blessed.' In Luke and in 1Co 11:24 He took bread and 'gave thanks.' "Every good gift and every perfect gift is from above, and cometh down from the Father of lights." Jas 1:17. This is God blessing us, and for which we in return bless God by giving thanks, by praise and worship.