I don't know why, but I'd never before realised that this is talking about spending time with God (amongst other things). What other motivation do you need to spend time with God? As with the vine, if you don't spend time with God you will wither up and die. Become miserable and lifeless. And you won't produce fruit.
I don't know why I've never realised this before. Love how God can nail you with a verse you already know quite well.
Will definitely be spending time with God tonight...

