For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.
How narrow is it? First, let's talk "in relation to". If you compare the width of Jesus to the width of every other man who ever lived, then it is narrow indeed! Just how narrow: as narrow as the mindset of those who will not believe!
On the other hand, how wide is it? As wide as Jesus' love! Wide enough that ALL who will believe can enter through!