Q. Why do Jews pray three times a day?
1. The first attributes the three services to the Patriarchs. Abraham who “rose early… to the place where he had stood before the Lord” (Gen. 19:27), instituted morning prayers; Isaac, who “went out to meditate in the field towards evening” (Gen. 24:63), introduced afternoon prayers; Jacob, who “happened upon a place” (or “entreated God who is in every place”) when the sun set (Gen. 28:11), created the evening prayers.
2. The second theory is that Shacharit and Minchah replace the daily offerings in the Temple. As there was no evening offering, Ma’ariv was originally not obligatory, though the evening Sh’ma was always required (Deut. 6:4-9; Mishnah B’rachot 1:1). The equation of prayer with sacrifices is suggested by Hosea 14:3, “We shall replace bullocks with the offering of our lips”, and the rabbinic comment, “Just as the service is called Avodah (Divine service), so is prayer Avodah” (Sifre to Deut. 2:13).