…prayer is the highest act of worship, as He the Exalted says: “To Him belongs the true call, whereas those whom they invoke besides Him never respond to them in any way” (al-Raʿd 13:14); and He also says: “So call upon Allah, devoting the religion purely to Him, even though the disbelievers dislike it” (Ghafir 40:14). Therefore, invoking anyone other than Allah is the *shirk* (associating partners with Allah) that He and His Messenger have forbidden. The particular practices that some people single out as the essence of shirk are not so; at most, certain elements of them may form part of shirk. The phenomenon varies in degree—some forms are graver than others, and Allah’s protection is sought. (20) His words, “And the proof is His saying, ‘Worship Allah and associate nothing with Him,’” show that the greatest command is *tawhid* (monotheism). Allah begins with “Worship Allah” and immediately follows it with “and associate nothing with Him,” before mentioning the other rights. By opening with the affirmation of tawhid and the prohibition of shirk, the verse establishes that tawhid is the most important duty He has enjoined and shirk the most serious sin He has forbidden. Allah always starts with what is most important, then proceeds to what is next in importance; this is the reasoning derived from the verse.