Why is The Shema Three Parts?

HEAR, O ISRAEL: THE LORD IS OUR GOD, THE LORD IS ONE. And thou shalt love the LORD thy God with all thy heart, and with all thy soul, and with all thy might. And these words, which I command thee this day, shall be upon thy heart; and thou shalt teach them diligently unto thy children, and shalt talk of them when thou sittest in thy house, and when thou walkest by the way, and when thou liest down, and when thou risest up. And thou shalt bind them for a sign upon thy hand, and they shall be for frontlets between thine eyes. And thou shalt write them upon the door-posts of thy house, and upon thy gates.

And it shall come to pass, if ye shall hearken diligently unto My commandments which I command you this day, to love the LORD your God, and to serve Him with all your heart and with all your soul, that I will give the rain of your land in its season, the former rain and the latter rain, that thou mayest gather in thy corn, and thy wine, and thine oil. And I will give grass in thy fields for thy cattle, and thou shalt eat and be satisfied. Take heed to yourselves, lest your heart be deceived, and ye turn aside, and serve other gods, and worship them; and the anger of the LORD be kindled against you, and He shut up the heaven, so that there shall be no rain, and the ground shall not yield her fruit; and ye perish quickly from off the good land which the LORD giveth you. Therefore shall ye lay up these My words in your heart and in your soul; and ye shall bind them for a sign upon your hand, and they shall be for frontlets between your eyes. And ye shall teach them your children, talking of them, when thou sittest in thy house, and when thou walkest by the way, and when thou liest down, and when thou risest up. And thou shalt write them upon the door-posts of thy house, and upon thy gates; that your days may be multiplied, and the days of your children, upon the land which the LORD swore unto your fathers to give them, as the days of the heavens above the earth.

And the LORD spoke unto Moses, saying: ’Speak unto the children of Israel, and bid them that they make them throughout their generations fringes in the corners of their garments, and that they put with the fringe of each corner a thread of blue. And it shall be unto you for a fringe, that ye may look upon it, and remember all the commandments of the LORD, and do them; and that ye go not about after your own heart and your own eyes, after which ye use to go astray; that ye may remember and do all My commandments, and be holy unto your God. I am the LORD your God, who brought you out of the land of Egypt, to be your God: I am the LORD your God.’

The superintendent said to them: “Say one blessing,” And they blessed. They recited the Ten Commandments (Exodus 20:2–13 (20:2–14 in NJPS) or Deuteronomy 5:6–17, “Hear, [O Israel . . .]” (Deuteronomy 6:4–9), “And it shall come to pass, if you hearken . . .” (Deuteronomy 11:13–21), “And the Lord spoke . . .” (Numbers 15:37–41). They blessed the people with three blessings: “True and enduring” [the blessing that follows the Shema prayer in the morning prayer service], Avodah [the blessing that many Jews say as part of the Amidah prayer calling for Divine acceptance of the Temple service], And the Priestly Blessing (Numbers 6:24–26). And on the Sabbath, they added a blessing for the [priestly] watch that was leaving.

Rabbi Yehoshua ben Korchah said: Why does Shema precede V'hayah im shamoa? So that one may accept the yoke of the kingdom of heaven first, And after that accept the yoke of the commandments. And [why does] V'hayah im shamoa [precede] Vayomer? Because V'hayah im shamoa applies during the day and at night, And Vayomer only applies during the day.

R. JOSHUA B. KORHAH SAID: WHY IS THE SECTION OF 'HEAR' SAID BEFORE 'IT SHALL COME TO PASS'. It has been taught: R. Simeon b. Yohai says: It is right that 'Hear' should come before 'And it shall come to pass' because the former prescribes learning and the latter teaching, and that 'and it shall come to pass' should precede 'And the Lord said' because the former prescribes teaching and the latter performance. But does then 'hear' speak only of learning and not also of teaching and doing? Is it not written therein, 'And thou shalt teach diligently, and thou shalt bind them and thou shalt write them'? Also, does 'and it shall come to pass' speak only of teaching and not also of performance? Is it not written therein, 'and ye shall bind and ye shall write'? — Rather this is what he means to say: It is right that 'hear' should precede 'and it shall come to pass', because the former mentions both learning, teaching, and doing; and that 'and it shall come to pass' should precede 'and the Lord said', because the former mentions both teaching and doing, whereas the latter mentions doing only. But is not the reason given by R. Joshua b. Korhah sufficient? — He [R. Simeon b. Yohai] gave an additional reason. One is that he should first accept Upon himself the yoke of the kingdom of heaven and then accept the yoke of the commandments. A further reason is that it [the first section] has these other features.