Fasting is essentially giving up food (or something else) for a period of time in order to focus your thoughts on God.
The corrupt thief is having a great and special day in his life and has invited other people like him and people he commonly lived with and invites them to a great dinner to introduce them to his new friend and now teacher.
In Jesus’ time, there was a particular group of people who were considered unwelcome. One of those groups was the tax collectors.
By this time in history, Jesus had already called several of his disciples, performed healing miracles, and delivered the oppressed.
Jesus and his disciples follow Jairus because something sad and painful has just happened.