Greetings in the name of our risen Lord!
When we read passages like John 9:41 it seems to suggest that if you don’t know or understand the Gospel, you aren’t held responsible for it (which would hold to the “age of accountability” doctrine of many churches). If it does, can it be used for the saving of those who are mentally unable to comprehend the necessity of salvation? This type of question arises because as Christians we want to engage our community (especially the unbelievers) in a way to defend our God as a loving God when the world says things like, “If he is a loving God why does he allow . . .?” We have to be careful not to misuse Scripture to alleviate the fears of nonbelievers that God is not a loving God.
God is a loving God, yet one who gives salvation on his own terms. In the passage from John, Jesus speaks to Pharisees who "see" God revealed in his Law, and then "see" themselves as righteously following the Law and gaining eternal reward. Notice how arguments over healing on the Sabbath precede these words. Jesus "blinds" the supposedly sighted Pharisees to expose their sinfulness to themselves. This is done to then bring true sight, wherein they might know their true condition and turn to God for mercy rather than to brag upon themselves.
All are accountable for their sins. Those who know the Moral Law from Holy Scripture are judged by it; those who do not are judged by whether or not they have always followed the Natural Law (conscience) which is written in their hearts, as Paul says in Romans 2:12-24. By inspiration of the Holy Spirit, the apostle parallels what Christ says in John 9, "If you call yourself a Jew..., if you feel sure that you are a guide to the blind and a light to those in darkness, that you can train the foolish and teach children because you have in the Law the embodiment of knowledge and truth--now, then, while you are teaching someone else, do you fail to teach yourself?" He continues, "You boast about the Law, but by breaking the Law you are dishonoring God."
Mental ability does not translate to saving faith. Believers are numbered among the infants and the elderly, among geniuses and among those in the end stages of Alzheimer's. Faith is not "irrational"; nor is it the product of human thought. It is the "gift of God (Ephesians 2:8-9)." Rather than "defending" God's Word, Christians should boldly live and proclaim it. His love for sinners is revealed in Christ, lived in us, and spread by the proclamation of his inclusive, yet exclusive Word. Unrepentant sinners should be offended by the Word – a Word designed to strike fear into their hearts, even as it brings comfort to those who know forgiveness through Jesus.
Jesus said to them, “If you were blind, you would have no guilt; but now that you say, ‘We see,” your guilt remains. – John 9:41 ESV
Your Servant in Christ,