The apostle is now going to speak extensively about revelation of salvation. There are two senses in which the words of this verse must be taken and applied.
Even when you are preaching the gospel, people cannot see it until God moves in the heart. Human beings are so stubborn, so proud, that they will not see it. What is this preacher talking about? This simplistic nonsense! Doesn't he know that we have got further degrees in this and in that. Why doesn't he use the language of scholarship and worldly scholarship? We can preach the gospel simply and fervently and yet the eye does not grasp the message of Christ, the ear does not hear the convicting words, telling you that you are a sinner and you need to repent and be saved.