The Torah commands a person to pray. This mitzva appears in the verse: “To love the Lord your God, and to serve Him with all your heart and with all your soul” (Deuteronomy 11:13). The Sages said: Which is the service of God that is performed in the heart?... It is prayer (Ta’anit 2a). This obligation is stated in general terms. In practice, it was instituted that one must pray three times on each day of the week: morning, afternoon, and evening; and pray an additional prayer on Shabbat and festivals, the Musaf prayer.