Our Gemara on Amud Aleph quotes a profound theological principle: "The seal of the Holy One, Blessed be He, is truth."
Let us delve deeper into this idea. The Likkutei Halachos (Birchos Hahoda’ah 6:29) illustrates how emes—truth—is embedded within Hashem’s very name. When Moshe asks how he should identify God to the Jewish people, Hashem responds (Shemos 3:14):
“Ehyeh-Asher-Ehyeh,” and continues, “Thus shall you say to the Israelites, ‘Ehyeh sent me to you.’”
This response is multilayered. Aside from Hashem identifying one of His names as Ehyeh, the phrase itself is self-referential. It means "I will be what I will be," implying an utterly independent Being who exists without change or inconsistency. Hashem is telling Moshe: You cannot fully grasp My name—that is, My essence—but you can understand that I am infinite and independent of all reality.
There is a direct link between this concept and truth itself. Truth is absolute and consistent. Hashem’s existence is truth because He is utterly and completely existent, the ultimate reality upon which all else is contingent. This idea is further reflected numerically: the gematria of Ehyeh (אֶהְיֶה) is 21. When multiplied—Ehyeh × Ehyeh ("I will be what I will be")—21 × 21 equals 441, which is also the gematria of emes (אמת), truth.
A name of God represents an aspect or expression of His essence. Just as a person's name is merely a reference to their deeper, more complex identity, so too, a Divine name conveys an attribute of Hashem while He Himself remains beyond complete comprehension. One may call a friend "Yehuda," but Yehuda’s true self is far more than the name or what others associate with it. Yet, through a name, we establish a relationship and gain some understanding of the person. This is how we must approach the names of God.
If a name conveys something about Hashem, what then is His seal? Keeping with the metaphor, the function of a seal is to ensure that something is unadulterated, authentic, and verifiably from its source. This could be an official seal on a royal decree or the famous jug of oil from Chanukah, preserved with the unbroken seal of the Cohen Gadol. Similarly, if one wants to know whether something is truly from God, it must bear His official mark—truth.
How do we recognize this divine seal? Rav Saadiah Gaon (Emunos V’deos III:1) explains that Hashem implanted within us a moral intuition—an innate sense of right and wrong. Deep down, truth has a compelling quality; it resonates in a way falsehood never can. It asserts itself in the end, provided we allow our hearts to feel, our eyes to see, and our ears to hear (Devarim 29:3).
Translations Courtesy of Sefaria, except when, sometimes, I disagree with the translation 
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Rabbi Simcha Feuerman, Rabbi Simcha Feuerman, LCSW-R, DHL is a psychotherapist who works with high conflict couples and families as well male sexual health. He can be reached via email at simchafeuerman@gmail.com