Halakhah for Taanit 3:20

The Rishonim disagree about whether there is a Torah commandment to pray every day. According to Rambam (Sefer Ha-mitzvot, mitzva 5), there is a biblical commandment to pray daily, as the Torah states (Shemot 23:25), “Serve God your Lord,” and (Devarim 6:13) “Revere the Lord your God and serve Him.” Although these verses contain a general commandment to serve God, they also include a specific commandment to pray. The Sages interpreted “service” (avoda) to mean worship through prayer, as it is written:  “Love God your Lord and serve Him with all your heart” (Devarim 11:13), and they explained (Ta’anit 2a), “What is serving with the heart? It must mean prayer.” By praying daily, one fulfills her biblical obligation to pray. To fulfill one’s obligation, one must begin with praise to God, then petition God for her needs, and conclude by thanking God for the good He has bestowed upon her. The Torah does not specify how long one’s prayers must be. Therefore, some shorten their prayers and others lengthen them, yet they all fulfill their biblical obligation (MT, Laws of Prayer 1:2-3). Later, the Men of the Great Assembly formulated a set prayer text, as will be explained below (section 6).