Now the serpent was more crafty than any beast of the field that the LORD God had made. And he said to the woman, “Did God really say, ‘You must not eat from any tree in the garden?’” — Genesis 3:1

The serpent's question—"Did God really say?"—strikes at the very foundation of faith. Satan's oldest trick isn't to deny God outright but to cast doubt on his word. Our Lord Jesus answered the same tempter not with debate but with Scripture: "it is written". The man of God who hides God's word in his heart is protected against the deceiver.