Joseph brought his sons Menashe and Ephraim before his ailing father Jacob so that he would bless them:

So he blessed them that day saying, "By you shall Israel bless, saying: May G‑d make you like Ephraim and Menashe." (Gen. 48:20)

"So he blessed them that day, saying…" - what is the meaning of "that day"? It would have sufficed to say "So he blessed them". Furthermore, where the word "saying" [in Hebrew, "emor"] is written [in the Torah] it is spelled without a vav whereas in our verse it is spelt with a vav; why is it different here?

When Jacob wished to bless Joseph's sons, he blessed them with the unification of above and below….

However, this is the mystical meaning: "So he blessed them that day" - what is "that day?" It is the mystery of the lofty spiritual level that is assigned over blessings Above.

This refers to bina of Atzilut, which is the source of the outflow of blessings for the worlds and sefirot below it.

"That day" is a day [i.e. a burst of light/revelation] within the supernal place which is called "that" [in Hebrew, "hu"].

When the word "day", in Hebrew "yom", is followed by the word for "this", "zeh", it refers to the sefira of malchut. (Ziv HaZohar) In regard to "zeh", our Sages declared: You can point to it with your finger and say, "here it is" (Shemot Rabba 23:15), and therefore it corresponds to malchut which is the revealed level.

But here the word "yom" ["day"] is followed by the word "hu" - meaning "that day" - without separating between them.

The word "hu" implies a level beyond the range of the person's perception. It is "that day" not "this day". Accordingly, it signifies the sefira of bina, which is distant from malchut.

But because there is no separation between "yom"and "hu", this indicates that the two levels [bina and malchut] merge into one.

So that malchut/"yom" merges completely into bina/"hu".

It was for this reason that when Jacob wished to bless Joseph's sons, he blessed them with the unification of above and below [bina and malchut] as one so that the blessings would be fulfilled.

Unification from Below to Above, and then from Above to Below….

After this, he included all of them [the sefirot] in one [array] and said, "By you shall Israel bless, saying…" What is the meaning of "by you?" It surely signifies the mystery of unity.

Explaining the verse as a whole, there are three levels of unification here with which Jacob imbued Ephraim and Menashe:

The first unification is "that day" the unity of Below with Above [malchut and bina].

Following this is a descent to the middle level.

This refers to the six sefirot from chesed to yesod, comprising Zeir Anpin.

This is why the word for "saying" ["l'emor"] is written with a vav.

This is because the letter vav is the sixth letter of the alphabet and signifies the six sefirot comprising Zeir Anpin. Furthermore, its shape - narrowing from head to foot - indicates a drawing down from a higher level (bina) to a lower level (malchut). This is the middle unification.

After this there is a further descent below to "by you" [in Hebrew, "b'cha"].

The numerical value of this word is 22 - alluding to the 22 letters of the Hebrew alphabet, which are the individual building blocks of Creation within malchut, from which the Ten Utterances with which the world was created (Avot 1:5).

And this is indeed the proper way - unification from Below to Above, and then from Above to Below.

The blessing that he gives them is "by you shall Israel bless" - as indeed we do. The custom on Friday night is to bless our sons with the words, "May you be like Ephraim and Menashe". The Zohar's meaning is this: first Jacob raised the boys up to the source of blessing (bina), so that they themselves should be blessed (thus, "…so he blessed them that day"). Next, he endowed them with the ability to draw down blessing, represented by the word for "saying", where the vav in the word indicates channeling down. Finally, he endowed them with the ability to instill this blessing to all creatures - represented by "b'cha" =22, which alludes to the 22 letters of the Hebrew alphabet through which all creatures in this world are created.

[Zohar I, p. 233a; translation and commentary by Moshe Miller]