Chidah: 3 Levels of Service

Mishnah, Tractate Avot, Chapter 1, Paragraph 2: Shimon the Righteous was a remnant of the Great Assembly. He used to teach: The world stands on three things: On the Torah, on the service [of God] and on acts of kindness.

Rabbi Chaim Yosef David Azulai explained this Mishnah:

Through Torah study, we serve God with our words.
Through prayer [literally, service], we serve God with our thoughts.
Through acts of kindness, we serve God with our deeds.