When you work with believers, your resources are vast; the Spirit and the Word operate to bring about change. Unbelievers have neither power at work in them. Moreover, the Christian counsellee possesses a regenerate nature capable of understanding and appropriating Biblical truth. Again, that is something the unbeliever does not have. According to Romans 8:8, “Those who are in the flesh cannot please God.” That fact underscores it all.
Then, what should you do to help unbelievers? The Bible tells you to pre-counsel (evangelise) them. Explain to him that God has the answers to all your problems. But they are not available to you. I must first spend time pre-counselling1 you so as to help make them available. We cannot begin counselling until this matter is settled.
Then, present the gospel. An unbeliever may think that some change he has made pleases God when, in reality, it does not. False assurance will lead him away from Christ.