Contradiction with Matthew 11:25
This verse suggests that God reveals truths to "babes" and hides them from the wise, while 2 Corinthians 4:3 suggests the gospel is hidden only to those perishing.
Matthew 11:25: At that time Jesus answered and said, I thank thee, O Father, Lord of heaven and earth, because thou hast hid these things from the wise and prudent, and hast revealed them unto babes.
Contradiction with Isaiah 29:11
This verse describes a sealed book that is not understood by anyone, whereas 2 Corinthians 4:3 implies understanding is limited to those perishing.
Isaiah 29:11: And the vision of all is become unto you as the words of a book that is sealed, which [men] deliver to one that is learned, saying, Read this, I pray thee: and he saith, I cannot; for it [is] sealed: [book: or, letter]
Contradiction with Proverbs 28:5
This verse states that those who seek the Lord understand all things, contrasting with the notion of the gospel being hidden as stated in 2 Corinthians 4:3.
Proverbs 28:5: Evil men understand not judgment: but they that seek the LORD understand all [things].