Who is able to see and understand spiritual truths? According to Dr. Martyn Lloyd-Jones in his sermon “The Example by Nicodemus,” it is only those who have the Spirit. This is seen in Jesus’s encounter with Nicodemus in John 3:9. Jesus repeatedly refers to spiritual truths, such as the Holy Spirit’s power of salvation and the necessity of the new birth. But Nicodemus is unable to understand that Jesus is referring to spiritual truths and not simply physical ones. In this, the great error of humanity can be seen in the attempt to understand all things according to human reason and intellect. Yet the Bible shows the folly of this, for only those who are truly saved can perceive the nature of spiritual reality. Even then, it is by faith that they believe, not by their own intellect. This means that believers and unbelievers alike can never rely on their own abilities to understand God, the world, and themselves, but they must rely on the revelation of God and the illumination of the Holy Spirit to overcome the sinful blindness. For, as this sermon on Nicodemus points out, it is only by God’s grace that He can be known as Lord and Savior.

http://www.mljtrust.org/sermons/the-example-of-nicodemus/