People can pride themselves on their open-mindedness and clear thinking on subjects of scientific study and yet be prejudiced and sloppy when it comes to Christianity.  Challenge them boldly to be open-minded and investigate the evidence thoughtfully, as they would their own field of study or knowledge.  A scientist first observes the evidence, then draws a conclusion about it, and finally tests his conclusion by experiment to see if he is right.

Encourage and challenge your contact to study the evidence for Christianity.  Good books would be "Evidence for the Resurrection" (J. N. D. Anderson), "Verdict on the Empty Tomb" (V.  Grieve) or "Man Alive" (E. M. B. Green).  He should come with an open mind and the prayer that God (if He is true) will help him to gain spiritual insight.  Then he must come to a conclusion.  But he will never be convinced until he has made the final "experiment", coming to God in repentance and faith to accept Jesus Christ.