Shlomo Hamelech thought that his superior wisdom would protect him from the pitfalls which the Torah specifies await the king who transgresses its limitations on horses, wives and wealth. Chazal (Midrash Rabbah Shemos 6:1) teach that when Shlomo violated the mitzvah of Lo yarbeh lo nashim, “He shall not have too many wives,” the letter yud of the word yarbeh (too many) came before the Almighty, bowed and said, “Ribon HaOlomim, Master of the Universe, Did You not say that no letter of the Torah will ever be abrogated? Yet Shlomo stands here and has nullified me. Perhaps today he is nullifying only one mitzvah, but tomorrow he might decide to do likewise with another mitzvah until, Heaven forbid, he will nullify the entire Torah!” Hashem replied, “Shlomo and thousands like him will be nullified (come and go), but not one point of you will ever be nullified.” (The yud will never be abrogated.)
The commentators ask the obvious question: Yarbeh is comprised of four letters. Why was the yud the one letter that took a stand? The Chida, zl, offers an insightful explanation which is as brilliant as it is simple. The sole reason that Hashem permitted David Hamelech and his son, Shlomo, to gain entry into Klal Yisrael was the yud. When Rus married Boaz, some protested that the Torah prohibits a convert from Moav from being accepted into the Jewish fold. Lo yavo Amoni u’Moavi b’k’hal Hashem; “An Amoni or Moavi shall not enter the congregation of Hashem” (Devarim 23:4). Chazal (Yevamos 76b) expound that this prohibition applies only to the males, and not to the women: Amoni v’lo Amonis; Moavi v’lo Moavis. Had it not been for the yud at the end of each word, which designates only the male converts as unacceptable, David and Shlomo would not have been permitted into the fold. Thus, it was for good reason that the yud claimed its honor. After all, it was the reason that Shlomo achieved status as a Jew.
The Lev Simchah observes (based on a commentary of the Sfas Emes) that one who sins annuls his letter in the Torah. This is based on the Sifrei Chassidus, which note that the Torah contains 600,000 letters, just as Klal Yisrael contains 600,000 neshamos. Thus, each Jew has his personal letter designated in the Torah, from which he receives spiritual sustenance. Shlomo Hamelech was endangering his letter yud by ignoring the Torah’s prohibition.
The Chafetz Chaim, zl, explains this further, asserting that even if one Jew were to violate or ignore one of the 613 mitzvos, it would not be negated because someone else would perform the mitzvah. The mitzvos that apply to the melech Yisrael pertain to one – and only one – person: the melech. Thus, if Shlomo would not fulfill the mitzvah, no one else could step in and save the day. If Shlomo ignored the prohibition, the mitzvah would be vacated, and, with it, a letter of the Torah.