I believe one should definitely investigate the claims made by anyone who wants people to give their lives over to him. This question has made many rounds through the ranks of professional psychologists many times. One of the many things they have consistently noted is that Jesus simply doesn’t fit the profile of someone who is mentally disturbed. Think about what symptoms you may know a mentally disturbed person to have and then compare them to who Jesus was. Contrary to mentally disturbed person, Jesus never displayed inappropriate emotions. Jesus was able to hold a rational conversation and he didn’t jump to faulty conclusions. He didn’t dress odd or have a weird diet. He had no difficulty in relating to others. In fact he was able to relate to all different kinds of people from all walks of life. When you compare who Jesus was to someone you know to be mentally disturbed, you’ll see that behaviorally, the two have nothing in common.
A second test you could use to see whether or not Jesus was insane or not, would be to investigate his actual claims. For example, let’s say I told you I was the President of the United States. Now if I was insane, I would surely believe that I was the President. However, you probably wouldn’t take my word at face value. You’d probably look to see if I lived in the White House. You’d ask where my Secret Service agents were, and probably watch the news to see if that was me giving speeches. It probably wouldn’t take you very long to realize I wasn’t the President. It is no different with Jesus. If Jesus simply claimed to be God, as some cult leaders do today, that wouldn’t mean very much. However, Jesus backed up his claims. He performed miracles never before and never since seen. He commanded the forces of nature and He even raised himself from the dead! If this wasn’t enough you could evaluate the things that he taught. People from all religions and all cultures agree that Jesus was one of, if not the single greatest moral teacher to have ever walked the face of the earth. Does it make sense that the greatest moral teacher of all time would be insane? I would argue no