EXOD354 When I searched for the most essential principle, the cornerstone of our religion, I found the wholehearted acknowledgement of God's unity to be its root and foundation. It is the very first of the Torah’s gates, and it is the acknowledgement of God's unity that separates the believer from the nonbeliever. It is the central truth of the religion; Whoever deviates from it will be unable to practice [his religious duties] properly or hold on to any belief. For this reason, the first words of God directed to us on Mount Sinai were: “I am Hashem your God.... Do not have any other gods” (Shemos 20:2-3), and later on He exhorted us through His prophet, saying: “Listen [Shema], Israel: Hashem is our God, Hashem is one” (Devarim 6:4). You must understand this section (the “Shema”) until its end, and see how its words proceed from subject to subject, covering ten subjects, corresponding to [the number of] the Ten Commandments. First, we are commanded to believe in the Creator, as it says: “Listen, Israel: Hashem.” The word “listen” [shema] is used here not in the sense of listening with the ear, but in the sense of believing in the heart, as in the verses: “We will do and we will listen” (Shemos 24:7); “Listen, Israel, and be careful to do it” (Devarim 6:3). Whenever the word “listen” is used in this way, the intended meaning is none other than to believe and accept. After being commanded to believe in the reality of Hashem's existence, we are then commanded to believe that He is our God, as it says: “... is our God.” Then we are commanded to believe that He is truly one, as it says: “Hashem is one.” After commanding us to believe in and accept the three fundamentals just mentioned, Scripture then moves on to what we must add to them, namely, the wholehearted love of God, in the inner life and the outer life, with our souls and with our might, as it says: “Love Hashem, your God with all your heart and with all your soul and with all your might” (ibid. 6:5). I will explain this, with the Almighty's help, in the Gate of Love of God. Scripture then goes on to caution us about the duties of the heart, saying: “These words which I command you this day must be on your heart” (ibid. 6:6), meaning that one should keep them always in one's heart and believe in them in the depth of one's being. Then Scripture proceeds to those duties of the limbs which require both knowledge and action, as it says: “Teach them to your children and [if you have no children] speak of them” (ibid. 6:7); to educate a child is not the only reason why an adult should study. Scripture then continues: “…when you are at home, when you are traveling on the road, when you lie down, and when you get up” (ibid.), for there is never anything to keep the heart and tongue from fulfilling their duties, as may happen to the other limbs. We have already discussed, in the Introduction, how the duties of the heart are perpetually binding. All this serves to reinforce what was stated in the previous verse (“These words which I command you this day must be on your heart”): By keeping these words on one’s lips continually, they are ever in one's consciousness, and one’s thoughts are never empty of God. This is like what was said by King David: “I have placed God always before me” (Tehillim 16:8), and by Scripture: “It is a thing very close to you, in your mouth and in your heart, that you can do” (Devarim 30:14). Scripture then proceeds from duties of the limbs [which require both knowledge and deed] to those which consist of action alone, and gives three examples: “[1] Bind them as a sign on your hand and [2] let them be a frontlet in the center of your head. [3] Write them on the doorposts of your houses and on your gates” (ibid. 6:8-9). The references here are to the tefillin, worn on the hand and head, and to the mezuzah, which bring one to remember the Creator, to love Him wholeheartedly, and to long for Him, just as lovers keep their love in mind. ... Scripture gives three [ways of remembering God], so that they be stronger and more lasting [in effect], as the Wise One [King Solomon] said: “A threefold cord is not quickly broken” (Koheles 4:12). This section thus covers ten subjects; five of them are spiritual, and five of them physical. The spiritual ones are: (1) Hashem exists; (2) He is our God; (3) He is one; (4) We should love him with all our hearts; (5) We should serve him wholeheartedly. The five physical ones are: (1) “teach them to your children”; (2) “speak of them”; (3) “bind them as a sign on your hand”; (4) “let them be a frontlet in the center of your head”; (5) “write them on the doorposts of your houses and on your gates.” Our Masters come of blessed memory, have said “Why is [the section of] ‘Shema’ placed before [the section] ‘if, then, you carefully obey [my commandments]’ (Devarim 11:13-21)? So that one first except accept upon oneself the yoke of God's kingship, and then accept upon oneself the yoke of the commandments.” (Yerushalmi, Berachos 2:2). It is for this reason that I have placed the Gate of the Unity of God before any other of the book’s gates.