We hear the call of the first disciples today, but it happens in a different way than it does in Matthew or Mark's Gospel.  It's more gradual rather than instantaneous.  That's important, because I think that is not all that different than how we have heard the call and responded.  

Peter reaches a tipping point and realizes not only who Jesus is, but also who he is.  And even more, he realizes what this invites him to.  And he's afraid.  Peter is not all that different than you and I in this regard.