The first guy promises to follow Jesus wherever he goes, but Jesus tells him that he's homeless and if the guy comes with him, he can expect to be homeless too. This guy hasn't thought it through. The cost of the kingdom is high.
Jesus tells the second guy to follow him, but he wants to bury his father first. (If the dude is dead and unburied, what is his son doing just hanging out? Or is he waiting for the undertaker to show up?) He wants the loose ends tied up. Jesus tells him to "let the dead bury their own dead," but the guy is to get busy proclaiming the kingdom. Whether the guy's request is "reasonable" or not we'll never know. But we do know that the need of the kingdom is immediate.
The third guy wants to follow Jesus but wants to say goodbye to his family first. Maybe he wants a foot in both worlds, the present age and the age to come. Either way, Jesus tells him that once he starts in the kingdom (presumably he already had), if he looks back he doesn't deserve to have a part in it. The demand of the kingdom is unyielding.
Its cost is high; its need is immediate; its demand is unyielding. Does my life reflect subservience to that particular kingdom today? Does yours?