The writing of Karen Armstrong actually notes the human views of the existence of God in three major designs of religious belief in the society today, namely that of the Judaism, Christianity and Islam.
One reason is that the roots of the Jewish religion go back some 4,000 years in history and other major religions are indebted to its Scriptures to a greater or lesser degree. Christianity, founded by Jesus (Hebrew, Ye‧shu′a‛), a first-century Jew, has its roots in the Hebrew Scriptures. And as any reading of the Qur’ān will show, Islām also owes much to those scriptures. (Qur’ān, surah 2:49-57; 32:23, 24) Thus, when we examine the Jewish religion, it could be noted that the roots of other religions are well examined just the same.
Simply put, Judaism is the religion of a people. Therefore, a convert becomes part of the Jewish people as well as the Jewish religion. It is a monotheistic religion in the strictest sense and holds that God intervenes in human history, especially in relation to the Jews. Jewish worship involves several annual festivals and various customs. (See box, pages 230-1.) Although there are no creeds or dogmas accepted by all Jews, the confession of the oneness of God as expressed in the Shema, a prayer based on Deuteronomy 6:4 (JP), forms a central part of synagogue worship: “HEAR, O ISRAEL: THE LORD OUR GOD, THE LORD IS ONE.”
This belief in one God was passed on to Christianity and Islām. According to Armstrong: “This sublime pronouncement of absolute monotheism was a declaration of war against all polytheism . . . In the same way, the Shema excludes the trinity of the Christian creed as a violation of the Unity of God.” The three major monotheistic religions of the world are Judaism, Christianity, and Islām.
But by the time Muḥammad appeared toward the beginning of the seventh century C.E., the first two religions, as far as he was concerned, had wandered from the path of truth. In fact, according to some Islāmic commentators, the Qur’ān implies rejection of Jews and of Christians in stating: “Not (the path) of those who earn Thine anger nor of those who go astray.” (Surah 1:7, MMP) Why is that?
A Qur’ānic commentary states: “The People of the Book went wrong: The Jews in breaking their Covenant, and slandering Mary and Jesus . . . and the Christians in raising Jesus the Apostle to equality with God” by means of the Trinity doctrine.—Surah 4:153-176, AYA. The principal teaching of Islām, for utter simplicity, is what is known as the shahādah, or confession of faith, which every Muslim knows by heart: “La ilāh illa Allāh; Muḥammad rasūl Allāh” (No god but Allah; Muḥammad is the messenger of Allah). This agrees with the Qur’ānic expression, “Your God is One God; there is no God save Him, the Beneficent, the Merciful.”
(Surah 2:163, MMP) This thought was stated 2,000 years earlier with the ancient call to Israel: “Listen, O Israel: Jehovah our God is one Jehovah.” (Deuteronomy 6:4) Jesus repeated this foremost command, which is recorded at Mark 12:29, about 600 years before Muḥammad, and nowhere did Jesus claim to be God or to be equal to Him.—Mark 13:32; John 14:28; 1 Corinthians 15:28. Regarding God’s uniqueness, the Qur’ān states: “So believe in God and His apostles. Say not ‘Trinity’: desist: it will be better for you: for God is One God.”(Surah 4:171, AYA)
However, we should note that true Christianity does not teach a Trinity. That is a doctrine of pagan origin introduced by apostates of Christendom after the death of Christ and the apostles.