Few things tug at the very core of the cosmos as much as we do, when we recite the Sh’mone Esrei. So let’s delve into that core-central prayer. But it’s important to understand a few things beforehand about the workings of the universe as Ramchal explains them.
We’re taught that G-d’s Ineffable name — which is composed of the four letters Yod, Hay, Vav, and Hay — forms the backdrop to all of creation. Now, the structure and makeup as well as the interactions between those four letters go to explain very many things about the overt and covert workings of the universe. But we’ll only touch upon these few facts about them for our purposes.
We also learn that G-d’s Providence reaches us primarily through three sources which are alluded to by the first three of the four Hebrew letters of G-d’s name. The three of them must be joined together on a very deep and wide esoteric level if that Providence is to reach us. And we’re also told that the final letter of G-d’s name, Hay, only comes into play once the other three are joined together.
And all of that is activated when we recite the first blessing of the Sh’mone Esrei which reads as follows (with some omissions): “Blessed are You, our G-d and G-d of our fathers — the G-d of Abraham, the G-d of Isaac, and the G-d of Jacob — the great, mighty, and awesome G-d … who recalls the Patriarchs’ acts of kindness, and will bring a Deliverer to their descendants …. “.
For we’re told that the three letters of G-d’s name under discussion are subtly alluded to by the terms “great, mighty, and awesome” there; and that they’re tied-in on an arcane level with the patriarchs Abraham, Isaac, and Jacob as well. What that comes to is this.
The term “great” alludes to G-d’s kindness (according to one kabbalistic system), which is represented by the letter Yod of His name and by the patriarch Abraham; “mighty” alludes to G-d’s judgment, which is represented by the (first) letter Hay and by the patriarch Isaac; and “awesome” alludes to G-d’s mercy, which is represented by the letter Vav and by the patriarch Jacob.
So when we cite Abraham, Isaac, and Jacob, we draw upon their many merits which then allow for G-d’s Providence to pass through the “pipes” of the letters Yod, Hay, Vav which have thus been united under the cumulative merits of the patriarchs.
The final letter, Hay, is activated by the statement later on in that blessing about G-d bringing a Deliverer to Abraham, Isaac, and Jacob’s descendants, since that alludes to King David, from whose line the Moshiach will come. David’s descendant will thus complete the role of the patriarchs, and will thus join all *four* letters of the Divine name together.
The Sh’mone Esrei’s middle blessings then help transmit G-d’s Providence through those “pipes”, and the last blessings allow that all to reach its intended recipients.