Midrash sa Jeremias 31:22: Midrash Tanchuma, Midrash Tanchuma Buber & Bereshit Rabbah

Another explanation of And I will bless those who bless thee (ibid. 12:3). The Holy One, blessed be He, said to him: I will cause a tribe to descend from among your sons that will bless Israel, and it will be called the tribe of Levi. “Master of the Universe,” he replied, “but who will bless that tribe?” The Holy One, blessed be He, responded: When they bless Israel, I will bless them, as it is said: So shall they put My Name upon the children of Israel, and I will bless them (Num. 6:27). The Holy One, blessed be He, said unto Israel: In this world the tribe of Levi will bless you, but in the world-to-come I Myself will bless you, as it is said: The Lord blessed thee, O habitation of righteousness, O mountain of holiness (Jer. 31:22).

Another interpretation (of Gen. 12:2): SO BECOME A BLESSING. The Holy One said to him: I am going to raise up a tribe from you so that it may bless Israel. And which one is this? The tribe of Levi, since that < is the one which > blesses Israel. Abraham said to him: Sovereign of the World, who is to bless that tribe? The Holy One said to him: When they bless Israel, I will bless them. Thus it is stated (in Numb. 6:27): THUS THEY SHALL SET MY NAME UPON THE CHILDREN OF ISRAEL, AND I WILL BLESS THEM. The Holy One said to Israel: In this world the tribe of Levi is blessing you in my name, but in the world to come I will bless you in my glory. Thus it is stated (in Jer. 31:22 [23]): MAY THE LORD BLESS YOU, O HABITATION OF RIGHTEOUSNESS, O HOLY MOUNTAIN.

The Holy One, blessed be He, declared unto Israel: In this world you fear sins, but in the world-to-come, where there is no evil inclination, you will tremble with joy over the benefactions reserved for you, as is said: Afterward shall the children of Israel return, and seek the Lord their God, and David their king, and shall come trembling unto the Lord and to His goodness in the end of days (Hos. 3:5). What is the meaning of His goodness? It refers to the Holy Temple, as it is said: That goodly hill country and the Lebanon (Deut. 3:25). The blessing comes from Zion, as is said: The Lord shall bless thee out of Zion, and thou shalt see the goodness of Jerusalem (Ps. 128:5). Dew is blessed from Zion, as is said: Like the dew of Herman, that cometh down the mountains of Zion (ibid. 133:3). Help comes from Zion, as it is said: Send forth thy help from the sanctuary, and support thee out of Zion (ibid. 20:3). Salvation comes from Zion, as it is said: Oh, that the salvation of Israel were come out of Zion (ibid. 14:7). The Holy One, blessed be He, said: In the world-to-come I shall bless you out of Zion, as it is said: The Lord blessed thee out of Zion; even He that made heaven and earth (ibid. 134:3). And I shall bless Zion, as is said: The Lord bless thee, O habitation of righteousness, O holy mountain (Jer. 31:22). Amen.