Question:
How can we keep our inability to understand from turning to unbelief?

Answer:
Doubt comes from the devil: (Satan tempting Eve, and other Scriptures.) We must accept the Word because God says so. (Matthew 21:21, 22; 2 Timothy 1:7; Isaiah 55:8; Romans 11:33,34; Deuteronomy 29:29.) If we lack wisdom we should ask God for it (James 1:5).

We cannot understand God’s truth by our intellect:  “For My thoughts are not your thoughts, neither are your ways My ways, saith the LORD. For as the heavens are higher than the earth, so are My ways higher than your ways, and My thoughts than your thoughts” (Isaiah 55:8-9). But God has been pleased to “reveal” His truth to faith by the Spirit (1 Corinthians 2:10). “Through faith we understand” (Hebrews 11:3). Thomas doubted (John 20), but Jesus told him to believe. “Faith cometh by hearing and hearing by the Word of God” (Romans 10:17). We need childlike faith. Jesus said this in Matthew 18:2,3. We should not be filled with doubt but simply believe what God says.