Being Comfortable is normally desirable, unless you're in a race or a war!

And the Bible compares our Christian life to both.

In a race you need to be training in order to build endurance and when you are running the race itself you push yourself to the limit in order to win. 

And in war, intense concentration and focus must be maintained in order not to get killed.  You don't get entangled in civilian affairs, you focus on the orders you've been given, and you carry out your mission.

So then why do we as Christians think we can get away with sitting around on the couch, or just earning a living?  We are in a war, and the souls of men are at stake. 

We do not have to fight it on our own, and we do not have to "work up" the emotions to stir us to the battle.  But what we do have to do is spend enough time with our commander to gain His perspective, to learn his ways ,and to feel his heart of compassion for those around us.

I know I should do more for the Kingdom of God, and I want to, but I don't really know where to start.

I think you may be getting a little carried away with the analogy.  We have to make a living, and there is not but so much time in the day.