They had to wonder why the gospel that was preached, while accepted by many, was also not accepted by many others. Jesus, a truly great preacher, addressed this issue in his parable about seeds and soil. What's really fascinating about this little story is that even his closest disciples didn't hear what Jesus was saying. The Word was spoken to them and they were only half awake. They heard it, but didn't catch it.
Some people come to listen with closed hearts.
They are like the beaten down path. No matter how good your message is it is like throwing seed on a sidewalk. It just sits there. Soon it disappears. It doesn't really get down in and start to grow.