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Judaism, Christianity and Islam are known as the three great monotheistic religions. The central premise of monotheism is that there is only one God. But what is meant by “one God”? Does “one God” mean that this God is the only true God and all other gods are non-existent?

Certainly, most Jews, Christians and Muslims would agree with this.

Or does “one God” mean both that God is alone as God and that he is one person?

This is the position of Judaism. It is also the position of Islam, although Jews and Muslims differ in how they understand God. Also, Muslims are adamant that God could never have a son. Yet this is a pivotal teaching of the Bible, both Old and New Testaments, as understood by Christians. With respect to Christianity, the majority position is that God is alone as God, but that he is tri-personal, existing as three co-eternal and consubstantial persons of Father, Son and Holy Spirit. For believing Christians, who hold both the Old and New Testaments to be inspired, it is the testimony of God’s Word that ultimately determines how we understand the God we worship. Let’s turn to that evidence.

As part of their Shema, Jews recite Deuteronomy 6:4. In the Jewish Publication Society of America translation, this verse reads: “Hear, O Israel! The Lord is our God, the Lord alone.”

Verse 5 reads: “You shall love the Lord your God with all your heart and with all your soul and with all your might.”

It makes sense that if you believe in only one true God, all of your religious devotion would be directed to that one true God. This is in contrast to the polytheistic religions that the nations around Israel adhered to. In polytheism, you would appeal to a god of rain to bring rain to your crops, to a god of fertility to bring you children and to a god of war to bring you victory in battle. But the God of Israel does all these things and thus is to be worshipped with all the heart, soul and might.

Jews and Christians agree that monotheism means at least this much: there is only one God. But does it also mean more than that?

The JPS translation includes a footnote to Deuteronomy 6:5 indicating that the statement following “Hear, O Israel!” can also be translated: “The Lord our God, the Lord is one”. The Christian ESV translation renders the confession of faith in this statement: “The Lord our God, the Lord is one”. Yet it too has a footnote and in this case three alternate translations are given: “The Lord our God is one Lord”; “The Lord is our God, the Lord is one”; “The Lord is our God, the Lord alone”. The last of these agrees with the choice made by the JPS translators.

Why the seeming uncertainty about how to translate this verse? It is because the Hebrew word echad can mean both “one” and “alone”. Here is it important to note that “one” and “alone” are related concepts. This is certainly the case in English, as the word “alone” is based on two words “all” and “one” thus “all one”.

So, to understand the nature of biblical monotheism we need to examine other passages. There are three other passages in the Old Testament that refer to the Oneness of God. Two are:

“And the Lord will be king over all the earth. On that day the Lord will be one and his name one.” Zechariah 14:9 ESV

“Did not he who made in the womb make him? And did not one fashion us in the womb?” Job 31:15

Here the “one” in the second line is God. These verses reinforce the case that the Bible teaches that God is one. As already stated, we need additional clarification to determine what “one” here means. There is one more verse, in Malachi, that states the Oneness of God. We’ll come back to that verse later.

A series of powerful passages in the Book of Isaiah stresses that God is alone as the One True God. Here is one particularly noteworthy example:

I am the Lord, and there is no other,
besides me there is no God;
I equip you, though you do not know me,
that the people may know, from the rising of the sun
and from the west, that there is none besides me;
I am the Lord, and there is no other.
I form light and create darkness,
I make well-being and create calamity,
I am the Lord, who does all these things.
Isaiah 45:5-7 ESV

For the full set of verses that stress that God is alone as the One True God, see Isaiah 37:16-20, 40:18-25, 41:4, 43:10-13, 44:6-8,24, 45:5-7,14,18,21-22, 46:9. Other passages make similar claims, such as Deuteronomy 4:35-39.

These passages help show that the claim in Deuteronomy 6:4 that there is only one God is not an isolated example in the Bible. Once again, we can see that biblical monotheism means at least that the God of Israel is the Only True God. But a Christian who believes in the Trinity would also agree with this and argue that the three persons of the Trinity are together the Only True God. Is this what the Bible has in mind? A God who exists in three persons?

The testimony of God’s Word allows us to be more specific. First, it is important to note that the Hebrew word translated in English translations as “Lord” (not simply “lord”) is the Divine Name Yahweh. It is Yahweh who is the God of Israel.

When God made his promise to David through the prophet Nathan that he would raise up a son after him to take his throne, he also revealed an important biblical truth: “When your days are fulfilled and you lie down with your fathers, I will raise up your offspring after you, who shall come from your own body, and I will establish his kingdom. He shall build a house for my name, and I will establish the throne of his kingdom forever. I will be to him a father, and he shall be to me a son …” 2 Samuel 7:12-14 ESV

We know from verse 11 that is it the Lord (Yahweh) who is speaking here. While there is an initial fulfilment of this covenant in David’s son Solomon, who succeeded his father as king of Israel, the larger fulfilment is in the Messiah, that is, Jesus Christ. This is confirmed by Hebrews 1:5 in the New Testament.

Since the passages in Isaiah confirm that Yahweh is God and that Yahweh alone is God, the language of the Davidic covenant establishes that this God who alone is God will have a Son. In other words, Jesus, although the Son of God, is not God. Moreover, Yahweh is one person.

How do we know that? Because Yahweh, even in the Old Testament, is referred to as “Father”.

It is now time to turn to the verse in Malachi:

“Have we not all one Father? Has not one God created us?” Malachi 2:10 ESV

Biblical Hebrew commonly uses parallelism, where a succeeding line or statement is synonymous with the previous one. Thus the “one Father” that the Jews worshipped (or that they ideally worshipped) is the “one God” who created them. In other words, the one God of Deuteronomy 6:4-5 is the Father alone. This also confirms that the God of the Bible is one person. In conclusion, biblical monotheism asserts both that God is God alone and that God is one person.

Is it really that simple? Yes, it really is.

The Apostle Paul confirms this in his first letter to the Corinthians, where he not only makes it clear that the gods worshipped by polytheists are non-existent, but that the One God is the Father and that in addition to the One God, there is Jesus Christ, who is Lord – that is to say, Lord and Master of believers, who was elevated to that status through his sacrifice on the cross (Philippians 2:9-11).

… we know that an idol has no real existence, and that there is no God but one. For although there may be so-called gods in heaven or on earth – as indeed there are many ‘gods’ and many ‘lords’ – yet for us there is one God, the Father, from whom are all things and for whom we exist, and one Lord, Jesus Christ, through whom are all things and through whom we exist.
1 Corinthians 8:4-6 ESV