And I shall be innocent of great transgression. Let the words of my mouth and the meditation of my heart Be acceptable in Your sight, O LORD, my strength and my Redeemer. This showed two ways God revealed His word. The written word seems to be better for evangelism and Christian growth, but remember, there were 2,500 years before there was any written word validated as inspired. His handiwork still shows His eternal power and deity.
Men are without excuse.
For I am not ashamed of the gospel of Christ, for it is the power of God unto salvation to everyone who believes, to the Jew first and also to the Greek. For since the creation of the world His invisible things are clearly perceived, being understood by the things that are made, even His eternal power and deity, so that they are without excuse. The potential is still there for men who have not heard the written gospel to be accused or excused by the law written on their hearts. The death of our Lord Jesus Christ has provided redemption for everyone.