Isaiah 44:20 exposes the self-deception of idolaters, answering the call to know and understand in Isaiah 40:21.

In Isaiah 43:10, God declares Israel as witnesses to know and understand Him—answering the rhetorical questions of 40:21.

Psalm 19:1-5 declares that creation testifies to God's glory, providing the evidence for the knowledge assumed in Isaiah 40:21.

Jeremiah 10:8-12 contrasts worthless idols with the true Creator, echoing the call to know God in Isaiah 40:21.

Romans 1:19-21 explicitly states God has made Himself known through creation, directly addressing the ignorance questioned in Isaiah 40:21.

In Jeremiah 27:5, God asserts He made the earth and gives it to whom He wills—directly reinforcing the creation foundation theme.

Acts 14:17 affirms God's witness through nature, answering the question in Isaiah 40:21 about whether people have heard or understood.

In Job 37:5, God's thunder and incomprehensible deeds echo the creation power implied in Isaiah's foundations of the earth.