...Another thing, unless it is in the Torah of the Lord, they desire it. For anyone who engages in Torah, the Holy One, blessed be He, fulfills his desires. Rabbi Eliezer says, "The people of Israel said before the Holy One, blessed be He, Master of the Universe, we want to engage in Torah day and night, but we have no free time." The Holy One, blessed be He, said to them, "Perform the mitzvah of tefillin, and I will consider it as if you were engaged in Torah day and night."
Rabbi Yochanan said, "From this verse: 'And it shall be for a sign upon your hand, and for a memorial between your eyes' (Exodus 13:9), we learn that whoever wears tefillin fulfills the commandment of Torah day and night." Rabbi Yehoshua said, "What Rabbi Eliezer meant was only for the nights when the mitzvah of tefillin is not fulfilled, except during the day, as it is said, 'And you shall observe this statute at its appointed time from days to days' (Exodus 13:10)."
Rabbi Eliezer asked him, "And what do you fulfill, while you engage in his Torah day and night?" Rabbi Yehoshua said to him, "This refers to the recitation of the Shema. If a person recites it both morning and evening, the Holy One, blessed be He, considers it as if he engaged in Torah day and night." Bar Kapara said, "Whoever recites two chapters of the Shema in the morning and two in the evening fulfills the commandment of Torah day and night."
Rabbi Berechiah said, "Even the patriarchs established the Mishnah that they would sit during the day for the portion that is taken from the night and during the night for the portion that is taken from the day." They asked Rabbi Yehoshua what a person should study in Greek wisdom. He said to them, "Go and see which hour is neither of the day nor of the night, and you may study then, as it is said, 'And you shall meditate therein day and night' (Joshua 1:8)."
He then returned and said to them, "A person should not teach his son Greek wisdom, nor even a craft that would cause him to neglect the study of Torah, even for an hour, as it is said, 'Therefore choose life' (Deuteronomy 30:19)." We learned that in the morning, one recites two blessings before and one after the Shema, and in the evening, two before and two after. This is so that the recitation of the Shema day and night will be equal, as it is said, 'And you shall meditate therein day and night' (Joshua 1:8)."
Rabbi Yossi said, "Based on the verse, 'Seven times a day I praise you because of your righteous ordinances' (Psalms 119:164), one should recite the Shema at least seven times a day."