The greatest hindrance to belief in the gospel does not arise from human intellect, but from the heart that has been darkened by sin. In this sermon on Ephesians 4:17–19 titled “Darkness and Light,” Dr. Martyn Lloyd-Jones highlights the warning of Christ that all people in their natural state are alienated from God and unable to pursue what is good and right. This is because the effects of the fall extend to every aspect of humanity. It corrupts the mind, hardens the heart, and distorts the will. Despite this fallen state, humanity still places great worth and confidence in their ability to reason and know morality. This is evident in the many great philosophers of the ancient world who after all their learning and knowledge were still never able to come to true knowledge of God. As Dr. Lloyd-Jones teaches, this shows that what people need is not simply more knowledge, but a new heart and mind that is freed from the mastery of sin and its domination. However, freedom from sin comes only through the gospel of grace and the sovereign working of the Holy Spirit. This is why it is so important to pray that God would work in the hearts and minds of others to reveal Himself to them and give them a true understanding of the gospel of Jesus Christ.

http://www.mljtrust.org/sermons/darkness-and-light/