The 5th mitzvah is that we are commanded to serve G‑d (blessed be He). This commandment is repeated many times: And you shall serve G‑d, your L‑rd”;1″And you shall serve Him”;2 “And to serve Him.”3
Although this commandment is of a general nature,4 as explained in the Fourth Principle,5 [and apparently should not be included in the count of the 613mitzvos,] nevertheless it has a specific quality, since it is the commandment to pray.
[We see that “service” is not just a general command from the following statements:] The Sifri6 says, “The verse, ‘And to serve Him’ means prayer.” The Sages also said, “The verse, ‘And to serve Him’ means Torah study.
In the Mishnah of Rabbi Eliezer, the son of Rabbi Yosi HaG’lili,7 the Sages said, “What is the biblical source to include prayer among the mitzvos? From the verse, ‘You shall fear G‑d, your L‑rd, and you shall serve Him.’ “8
They also said,9 “Serve Him through His Torah; serve Him in His Temple.” This [statement, ‘serve Him in His Temple,’] means that one’s goal should be to pray in the Temple or in the direction of the Temple, as King Solomon explained.10