Question: "What does it mean to have a reprobate mind?"
Paul describes two men named Jannes and Jambres as those who “resist the truth: men of corrupt minds, reprobate concerning the faith" (2 Timothy 3:8). Here the reprobation is regarding the resistance to the truth because of corrupt minds. In Titus, Paul also refers to those whose works are reprobate: “They profess that they know God; but in works they deny him, being abominable, and disobedient, and unto every good work reprobate” (Titus 1:16). Therefore, the reprobate mind is one that is corrupt and worthless.
As we can see in the verses above, people who are classified as having a reprobate mind have some knowledge of God and perhaps know of His commandments. However, they live impure lives and have very little desire to please God. Those who have reprobate minds live corrupt and selfish lives. Sin is justified and acceptable to them. The reprobates are those whom God has rejected and has left to their own devices.
Can a Christian have a reprobate mind? Someone who has sincerely accepted Jesus Christ by faith will not have this mindset because the old person with a reprobate mind has been recreated into a new creation: “The old has passed away; behold, the new has come” (2 Corinthians 5:17). Christians are basically “new” people. We live differently and speak differently. Our world is centered on our Lord and Savior, Jesus Christ, and how we can serve Him. Also, if we are truly in the faith, we will have the Holy Spirit to help us live a God-honoring life (John 14:26). Those with reprobate minds do not have the Spirit and live only for themselves.
Recommended Resources: A Godward Life by John Piper and Logos Bible Software.