Some folks just won't believe. It doesn't matter what they see or what others say; they are determined not to believe in Jesus. How do we explain this kind of thing? People have to will to do God's will if they are going to believe! If they play with sin, they open their hearts for Satan to block their believing. Sometimes, more often than we would like to imagine, religion can be a tool of Satan's to contribute to unbelief. Something like that happens here. However, we don't give up because God can use the circumstances in people's lives to open their hearts. We are not sure how many of the skeptics and unbelievers at this stage of Jesus' ministry became believers at Pentecost (see Acts 2).