DEUT198 Believe that Hashem is One. This idea is the most fundamental principle of the truth faith. It is the fixed pillar upon which the hearts of all sensible people rely. Our Sages teach (Berachos 61a) that each of us must be ready to give up his life for this principle--that Hashem is the One and unique God--for all who do not acknowledge this truth are considered as having denied the Jewish faith’s central principle. This is so because Hashem's rule over the universe is perfect and complete only by virtue of His Absolute Oneness. That is, His sovereignty is complete only because He alone creates and gives everything its existence, without any other power acting as His partner. If someone does not believe in this truth, he nullifies a positive commandment of the Torah. And so doing, he transgresses the entire Torah, for all of its commandments are dependent upon belief in the One and Unique God. Such a person denies the root principle of our faith and is not reckoned as a member of the Jewish People. He is considered a heretic. Conversely, he who fulfills this mitzvah, for he believes and trusts in the One God, is elevated to supreme heights. This mitzvah is one of the Torah’s six “constant” commandments. We are obligated to fulfill this precept at all times, without any interruption. [See Mishnah Berurah, Siman 1 in the Biur Halachah, s.v. Hu klal.]