Here a disciple is willing to follow Jesus at an easy level, walking across the lake. Jesus leads, they follow. When on the other side of the lake, Jesus explains the next place to follow Him. This principle is that when following Jesus, the agenda is ALWAYS set by Jesus. A teacher of the law is willing to follow wherever Jesus goes. Jesus ups the ante with telling this man (who followed across the lake) that you will have no home, and have a life of camping. This goes counter to the prevailing times where a Rabbi was responsible for feeding and housing his students. The expectations of following Jesus are changed to fit the person's need for growth.

Another disciple asks to finish taking care of his dad before following Jesus, kind of "hold my place in line". Jesus tells him that you must leave behind your family. This is Jesus setting the standard, and taking away the things we value more than Him.

In both of these cases, Jesus is simply asking of them what He did of His disciples in Matthew 4:19-22. The implication is, these two followers couldn't meet the more demanding criteria His other followers had already passed. In Matthew 9:9, the call of Matthew is found, so it also seems that there were spots available to be filled at this juncture of Jesus' ministry, just not by followers with lesser commitment.

Matthew 8:18-22