Deuteronomy 4:39
Know therefore this day, and consider it in thine heart, that the LORD he is God in heaven above, and upon the earth beneath: there is none else.
Primary
What this passage establishes
The LORD is God in heaven above and earth beneath, with no other beside Him.
Why it matters in the argument
This establishes the controlling biblical confession: every later passage about Father, Son, and Holy Ghost must be read without multiplying the one God.
Apostolic connection
Apostolic teaching begins with the Bible’s own insistence that God is one indivisible divine being, then reads the incarnation as that one God revealed in Christ.
Common misunderstanding
Counting titles, manifestations, or relational language does not overturn the Bible’s explicit statements that God is one and alone.
How to use it in conversation
Start here before discussing difficult relational texts. Establish what Scripture says plainly about how many are God.