Winston Churchill said that the Americans and British were “two great peoples divided by a common language.” In a similar manner, Judaism, Christianity, Islam and Zoroastrianism are four great religions seemingly divided by a common belief in one God.

Each of these great religions makes its own distinctive contribution to monotheism. Judaism has been called an ethical monotheism. Christianity teaches that the one God is three Persons. Islam unifies all life under the one God. Zoroastrianism, the fourth and often forgotten monotheistic religion, provides an ethical dualism.

The hallmark of Judaism is the Shema (Deut 6:4): “Hear, O Israel, the Lord our God is one God.” Abraham J. Heschel observes in Between God and Man: An Interpretation of Judaism: “Monotheism was not attained by means of numerical reduction. … One means unique … God is one means He alone is truly real … He is a being who is both beyond and here, both in nature and history, both love and power, near and far, known and unknown, Father and Eternal. … His is only a single way.

Thus the ethical monotheism of Judaism drives toward a morality: “And what does the Lord require of you, but to do justice, and to love kindness and to walk humbly with your God?” (Mic 6:8). To worship the one God means to walk (halakah, law) in the ways lovingly provided by God.

Christianity maintained the Jewish belief in one God while developing the doctrine of Trinity. The One God of Israel was incarnate in Jesus Christ: “In the beginning was the Word, and the Word was with God, and the Word was God … And the Word became flesh and lived among us” (Jn 1:1, 14). In addition to the Father and Son, the Holy Spirit was conceived as fully personal, not merely an emanation of God.

Thus Tertullian writes in Against Heresies (c. 190 A.D.): “The Church … has received from the apostles and their disciples this faith: in one God, the Father Almighty, maker of heaven and earth …; and in one Christ Jesus, the Son of God, who became incarnate for our salvation; and in the Holy Spirit.” The classical doctrine of Trinity is not about arithmetic, but about God’s rich Personhood and God’s economy of salvation.

Contemporary Trinitarian reflection attempts to recast this doctrine in ways that are not patriarchal, hierarchical or monarchial. Some theologians use the classical notion of perichoresis (shared life of the three Persons) to develop an understanding of Trinity as inclusive community that has strong implications for Christian practice.

Jurgen Moltmann writes in his The Trinity and the Kingdom of an “open and inviting Trinity” that “wants human freedom, justifies human freedom, and unceasingly makes men and women free for freedom.” Catherine Mowry LaCugna claims in God For Us: The Trinity and Christian Life that “the Trinity is a practical doctrine with radical consequences for the Christian life … a teaching about God’s life with us and our life with each other. Trinitarian theology could be described as par excellence a theology of relationship.”

Islam’s belief in monotheism is called Tawheed. The Quran says, “He is God, the one! God the eternally sought of all! He begets not and neither is He begotten. There is none like Him!” (112:1-4). Muslim scholar Abu Ameenah Bilal Philips notes three aspects to belief in one God:

  • oneness of the Lordship of God: there is only one Creator, Sustainer and Sovereign of the universe;
  • oneness of the worship of God: all worship should be directed only to God for only God is worthy of worship;
  • oneness of the names of God: God must be described in the way God has been revealed and in no other way.

Islam’s belief in one God leads to the unification of all of life through submission to God.

The monotheism of Zoroastrianism is an ethical dualism. Zoroaster (c. 628–551 B.C.) taught belief in the one God Ahura Mazda (Wise Lord). In the Gathas (a collection of hymns), Zoroaster proclaims: “What artist made light and darkness, sleep and waking?  Who made morning, noon, and night …? I strive to recognize by these things thee, Oh Mazda, creator of all things.”

Belief in the one God leads to choosing the Truth instead of the Lie in the great cosmic struggle of good against evil. Zoroaster had a complex explanation of God’s actions. Ahura Mazda is expressed through a Holy Spirit (Spenta Mainyu) and through modes of divine action, called Amesha Spentas. These have ethical qualities, such as Good Thought, Right and Piety.

John Noss writes in Man’s Religions: “Zoroaster gives us a rich conception of deity without abandoning monotheism.”

All four great monotheistic religions agree that the One God should be truly worshiped, rightly followed and ethically served.

James Browning is senior pastor of Englewood Baptist Church in Kansas City, Mo.

For further reading on the history of monotheism, see Karen Armstrong’s A History of God: The 4,000-Year Quest of Judaism, Christianity and Islam.

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