Inserting the Letter Yud in Pinchas
In last week’s parsha, the Torah records the incident of a Jewish prince named Zimri who consorted with a Midianite princess named Cozbi. Pinchas, a zealot, kills them. In this week’s parsha, G‑d rewards Pinchas for his brazen act of bravery and zealousness.
According to the Midrash, Pinchas was rewarded not only with the priesthood but also with a name change. The name Pinchas can be spelled two ways in Hebrew, with or without the letter Yud. As a reward for his holy deed, G‑d inserted a Yud, the initial letter of His Divine name, into Pincha’s name.
This Divine imprimatur allayed the concern of Pincha’s critics that his action was motivated by cruelty. G‑d added the Yud to underscore that Pinchas acted solely out of zealous devotion to the Torah’s laws that prohibited immoral and illicit liaisons.
The following is a further explanation adapted from the work Even Shlomo [by Rabbi Shlomo Zalman Ehrenreich, a Hungarian rabbinic leader, murdered in the Holocaust].  
The numerical value of Pinchas’ name with the added letter Yud (208) is the same as that of the Patriarch Yitzchak, who personified the Divine attribute of Gevurah-severity and judgment. Pinchas’ violent act required him to channel Yitzchak’s trait of Gevurah. Pinchas, however, was a grandson of Aaron, who more than any other Biblical figure personified the attribute of Chesed-kindness. When Pinchas killed Zimri and Cozbi, he demonstrated his ability to override his Chesed-personality and nature in the pursuit of G‑d’s will. Pinchas was not motivated by his own nature but by his obsession with responding to the Divine calling.
This explains why G‑d inserted a letter of His own name, the first initial of the Tetragrammaton. This name combines the words was [past], is [present] and will be[future], referring to the aspect of the Divine that transcends time and nature.
In order for Pinchas to do what he did required that he be connected to that aspect of the Divine that transcends nature.
Even Shlomo provides us with an even more intricate understanding of Pinchas’ connection to the Patriarch Yitzchak. The following is an adaptation of his explanation.
The Reader of the Letter
When Pinchas heard of the immoral behavior of Zimri and Cozbi he approached Moses for guidance. Moses did not have an answer for him. Pinchas reminded Moses’ teaching that this brazen act of immorality called for an extremely harsh response. Moses said to him, “The reader of the letter should be the one to implement it.”
What did Moses mean by the reader of the letter? Why didn’t he just say, “The one who remembered the law shall be the one to carry it out?”
To explain Moses’ response, Even Shlomo refers to a Talmudic tradition that before G‑d gave the Torah to the Jewish people He raised the mountain over their heads and threatened to drop it on them if they did not accept the Torah.
The Midrash Tanchuma asks “but doesn’t the Torah state that when Moses approached the Jewish people concerning the Torah they responded enthusiastically, “We will do and we will hear?” This meant that they were prepared to accept the Torah even before they knew what was in it.
The Midrash Tanchuma answers that they were only prepared to accept the Written Torah, not the Oral Torah.
The distinction they drew was that the Written Torah, comprising the Five Books of Moses, were G‑d’s explicit words as He dictated them to Moses. Moses was no more than a conduit for the Divine words. This they were eager to accept.  To them it was a direct and unambiguous communication from G‑d. Moses, in their eyes, was no more than G‑d’s mouthpiece.
The Oral Torah, by contrast, is filled with ideas that have been transmitted generation to generation though human intervention. In this process, there is a risk that G‑d’s precise wording to Moses can get scrambled or even lost. Moreover, the Oral law consists of our Sages’ interpretation of the laws and their application to new and developing situations. Consequently, G‑d’s word is filtered through the intellect and scholarship of mere mortals.
The Jewish people resisted this part of Torah because, to them, it was not unequivocally G‑d’s clear teaching.  They preferred that the Oral Torah also be enshrined in a canonized text, safeguarding G‑d’s exact words.
Heavenly Mountain
G‑d dangled the mountain over the Jewish people to disabuse them of their erroneous distinction between the Written and Oral Torahs.
The imagery of suspending the mountain over their heads can be explained metaphorically, showing the way it addressed their concern.
They were prepared to accept a Written Torah because it came to them from Above. In other words, with the Written Torah they did not have to toil and struggle to discover the truth of G‑d’s word. After all, it comes down to us from Above. We just sit back, passively, and accept what G‑d gives us. It makes life much simpler, knowing that we are guided by a Divine hand.
The Oral Torah, by contrast, requires that we climb an intellectual, emotional and spiritual mountain.  We must invest our own effort and energy into this task, sometimes remaining in the dark when we fail to reach the summit. Indeed, there are times when the Talmudic Sages, the transmitters of the Oral Torah, could not figure out the proper answer to some legal dilemma.  They would conclude the issue by stating teiku, which stands for “Elijah [in the Messianic Age] will resolve all the questions and queries.”
How did G‑d assuage the Jewish people about their concern, predicated as it was on the desire to have a clear and unambiguous communication and relationship with G‑d? They were loath to relate to G‑d, or have G‑d relate to them, in indirect and vague ways.
To allay their concern, G‑d placed the mountain over their heads to show them that the Oral Law—the Mountain—is no less Divine than the Written Torah. It too comes from “above” notwithstanding the fact that G‑d chooses to channel it through the Sages of every generation.  G‑d, in His infinite wisdom, knows that when the Torah enters the minds of humans there will be multiple results, questions and arguments. In effect, the questions themselves are just as Divine as the statements that were questioned. Moreover, the conflicting opinions are equally Divine, as the Talmud states concerning the disputes between the School of Shammai and the School of Hillel: “These and these are the words of the living G‑d.” All of the Oral law, all its disputes, questions and ambiguities are like mountains that are above us; they are equally from G‑d Above.
This explains why Moses told Pinchas that “The reader of the letter should be the one who implements it.” The difference between the writing of the letter and the reading of the letter is the difference between the Written Torah and the Oral Torah, which requires understanding and interpretation.
Zimri’s implied argument as he consorted with Cozbi was that no written commandment prohibited his action. The prohibition of his indiscretion was rooted in the Oral tradition, and thus was subject to human reading and understanding. Pinchas appreciated the true value of the Oral Torah; it is no less Divine and authoritative than the Written word and thus embodies G‑d’s express commandments. Moses stressed that “The reader of the letter should implement it.” Pinchas was eminently qualified to carry out the punishment because he was doing it out of respect for G‑d’s as expressed in the Torah and not on his whim or personal feeling.
Connection to Yitzchak
This helps us appreciate the connection of Pinchas to Yitzchak.  When G‑d told Abraham to sacrifice Yitzchak, he was prepared to do so even though the very thought of what he was told to do contradicted everything he knew; Abraham accepted the awful charge because he heard it directly from G‑d. For Abraham, this was like the Written Torah which conveys G‑d instructions verbatim.
Yitzchak, on the other hand, heard about his ordeal from Abraham, who transmitted it to him. This was a process more akin to the Oral law. The fact that Yitzchak was prepared to accept this indirect and enigmatic command from G‑d was a testament to his fidelity to the word of G‑d, even when it was conveyed indirectly.
What makes this aspect of the Oral law so challenging is that it demands effort and struggle on our part.
Parallels to the Bais Hamikdash and Moshiach
We can find a parallel in the relationship of Jerusalem and the Bais Hamikdash, the location of which is not mentioned explicitly in the Torah. The prophet Samuel and King David had to search far and wide for clues until they found Mount Moriah and realized that this was the place where G‑d wanted His temple.
The same is true for the Davidic dynasty that lies between King David and Moshiach. It was not demonstrably clear in the moment from the Torah who the chosen monarch should be. The prophet, whose words we recite every month when we bless the new month, stated “And they searched for their G‑d and for their King David.” Our efforts to bring Moshiach require that we search for the signs for the Messianic Age and for Moshiach.
Once we do our part in hoping, praying, anticipating and doing everything in our power for the Redemption, G‑d will reveal His “hand” and make it clear that our search was not in vain. G‑d will crown our efforts with success.
According to Maimonides, the Bais Hamikdash will be built by the Jewish people under the direction of Moshiach. On the other hand, Rashi opines that it will descend from Above.
The Rebbe has reconciled these two opinions. The Bais Hamikdash that will come from above will descend into the Bais Hamikdash which we will construct.
The entire process of bringing Moshiach and Redemption requires our maximum effort, which will frequently involve searching for the light in the darkness. In the end, it is that search and struggle for Redemption that will get us out of the muck of Galus and prepare us for the revelation from Above.  
Pinchas thus teaches us that we must search for and discover G‑d’s will when it is not clearly spelled out in the Torah.

We can now understand the statement of the Zohar that Pinchas and Elijah, who will usher in the Messianic Age, are one and the same person.  Pinchas paved the way for the acceptance of and dedication to the Oral Torah.  He will therefore also be the one who will resolve all of the difficulties in the Oral law, and show us how it is utterly and demonstrably Divine.