What does Luke 9:18 mean?
Jesus gave the Twelve power to heal diseases, expel demons, and raise the dead (Matthew 10:8). Then He sent them off to preach the kingdom of God has come (Luke 9:1–6). Herod Antipas, ruler of Galilee, heard what they were doing and became confused about who Jesus is. Herod seems to think Jesus is either John the Baptist raised from the dead or another prophet working in the same spirit as John (Mark 6:16; Luke 6:7–9). The people are divided between Elijah, John, or some other Old Testament-era prophet (Luke 9:19).The term "alone" must be qualified. Often, crowds so surround Jesus—squeezing, pushing, grasping—that He teaches from a boat (Mark 3:7–10) and has no time to rest or eat (Mark 3:20). "The disciples" certainly include the Twelve, but other faithful followers might also be with Him; Luke doesn't restrict "disciples" to the Twelve (Mark 4:10; Luke 8:9). Even if Jesus is surrounded by fifty of His closest followers, it feels like He's alone compared to being crushed in a crowd.
The Gospels do not necessarily keep the events of Jesus' ministry in chronological order. Precise timelines were not as important to ancient writers as modern journalists. Luke sought to write an "orderly account" (Luke 1:3), which implies intentional organization of some sort, but not necessarily narration of events in timeline fashion. It is, however, interesting to compare Luke's sequence of events to John's. Matthew, Mark, and John line up Jesus feeding the five thousand, walking on water, returning to the west coast of the Sea of Galilee, then re-engaging the crowds.
In John's account, Jesus' identity is given a longer discussion. The people want to make Him king because He has provided food (John 6:15, 26). Through the course of the ensuing conversation, Jesus identifies Himself as the Son of God, the provider of God's bread, the bread of life, and the one who brings resurrection. He then says that anyone who eats the bread of His flesh and drinks His blood will have eternal life. His words are so shocking, many of His disciples abandon Him (John 6:25–66).
It is then that Jesus asks the Twelve what they think. Peter responds, "…we have believed, and have come to know, that you are the Holy One of God" (John 6:69). The crowds would like to keep Jesus restricted as "only" a restoration of the Old Testament prophets. They would even accept Him as an earthly king, if He took care of their material needs. They cannot accept Him as the Christ intended by God: a spiritual Savior.