Oooh, I love this thread. It sounds deliciously revolutionary.
*warning - rant ahead*
There are a lot of lies around. Many people want to entice you into their addictions. The worst lie of all is wanting to make a difference - the ultimate seduction to cheat death.
All you have to do is work very hard in your chosen profession; be exploited; work 24/7 (and don't delude yourself, you will); try to climb the ladder; become addicted to status and toys and stuff; pay lots of taxes; contribute to someone's bottom line; delight your mother and father (who did the same as you are doing but failed); get a mortgate (delighting your bank's shareholders); have kids and sacrifice EVERYTHING for them; feel trapped; face the growing realisation that actually you won't make a difference AND that you probably had your ladder up against the wrong wall in the first place; get depressed; project all your unfulfilled needs onto your children and....well you know the rest.
Firstly, know that if you do make a difference it won't make you happy.
Secondly, maybe the problem is less that you find it difficult to get motivated than actually you are postiively demotivated at the path that seems to lie before you e.g. the school, university, job, material conformity path.
Thirdly, dream. Go wild. Ask yourself the question - if I had everything I needed or wanted, what then would I do? If I had made a difference, loved my neighbour, delighted my parents, made the money, got the degree - what would I do then?
The most scary thing in my view is to shake off those horrible expectations and do what you want - if that means lying on your bed thinking all day, then do it. And see where it takes you. And enjoy the journey.
*rant over*
Oh, btw, I am a Christian too. Though how that matters I'm not quite sure