Pentecost +4 – Year A
While it is fun to eternally play with the "Why" questions of life that will seemingly never be settled, even with cute retorts about physicians and bridegrooms, the larger parenthesis of this passage is that of action.
We begin with a not-so-innocent bystander minding his own tax forms and everyone's, who is called to action – "Follow" – and he does.
We end with caller being called. "Follow", says another official to Jesus. And follow Jesus does. Even with delays along the way Jesus follows. He follows into a present past and then leads to call again from an unexpected future.
Between calling and being called there are those fun questions of "Why?" For the moment put them aside for if they are not able to be treated as poetry they will eternally trip us up and divide us.
Another take would have Jesus learning the mercy he claims G*D desires. This mercy shows a new way of doing business – a caller is ready to be called. It is so easy to claim that a caller has priority over the called. It is a mercy to not be trapped into a position, even one as exalted as Messiah. Hear again how Jesus is called away from teaching to living his teaching with his action. Mercy entails life changes in the face of other plans that had been made.