Galatians 3:17 establishes that the law cannot annul the promise — verse 20 then explains this by noting the law had a mediator while the promise came directly from the one God.

Genesis 15:18 records the covenant God made directly with Abram — the very promise that Paul argues in Galatians 3:20 was given without a mediator, emphasizing God's oneness.

Deuteronomy 6:4 is the Shema — 'The LORD is one' — which Paul directly echoes in Galatians 3:20 to conclude his argument about the law and promise.

Romans 3:29 uses the same 'God is one' argument to include Gentiles — reinforcing the implication from Galatians 3:20 that God's oneness makes the promise universal.

1 Timothy 2:5 explicitly states there is one God and one mediator — directly extending Paul's logic from Galatians 3:20 that God's oneness implies a single mediator.

Romans 3:30 uses the same 'God is one' argument to show God justifies both Jews and Gentiles by faith.

Genesis 17:2 describes God making a covenant directly with Abraham — consistent with the direct promise that Paul contrasts with the mediated law in Galatians 3:20.

Job 9:33 laments the lack of a mediator between Job and God — the same concept Paul uses in Galatians 3:20 to contrast the mediated law with the direct promise.

James 2:19 also affirms 'God is one' but warns even demons believe—showing monotheism alone doesn't save.