What does Luke 9:15 mean?

A crowd of five thousand men, plus women and children, surround Jesus and the disciples in an unpopulated area near Bethsaida (Matthew 14:21). The people are hungry, as they've been with Jesus all day. The disciples want Jesus to release the people to go to the small towns to find food to buy. Jesus has other plans (Luke 9:10-14).

When Jesus heals and teaches, the people often crowd around Him. At least once, He had to climb into a boat and teach from the water so everyone on shore could hear (Mark 4:1). On another occasion, the people pressed in around Him so much Luke describes it with the Greek word for choking (Luke 8:42). There's no reason to expect these people are much different, yet they obey the disciples and move away. Perhaps they sense they are going to get food.

Jesus is inviting the disciples into kingdom work without explaining what He's going to do. The disciples don't understand, and they don't exactly trust Jesus to address their concerns. However, like the people, they obey. Later, the disciples will bicker over personal glory (Luke 9:46–48). They serve others in the context of direct obedience to Christ, not yet understanding Christ is calling them to be servants.