I carefully re-translated this very literally (making it a bit awkward in English), to make sure there is no ambiguity:
And the apostles say to the Lord, "Add faith to us." Yet the Lord says, "If you were having faith as a kernel of mustard you would have been saying ever to this sycamore-fig tree, 'Be being uprooted and be being planted in the sea,' and it would ever obey you. Yet who out of you having a slave plowing or shepherding, who comes out of the field, will declare immediately, passing by, 'Recline'? Contrariwise, no, he will declare to him, 'Make ready what I should be dining and, being girded about, be serving me, until I may eat and drink and, after these, you shall eat and drink.' He is having no favor to that slave, since he does the [things] prescribed to same. I think not. And/also thusly you, whenever you may do all the [things] prescribed to you, be saying, 'Consequently, unprofitable slaves we are being; because that we have been being obligated to do, we have done.'"In Luke 17, lots of people miss the point of this illustration. The disciples ask, "Lord, increase our faith!" What kind of a question is that, to begin with, anyway? Isn't "faith" (i.e. to believe) our part of the deal?
Here's the illustration I like to use:
Suppose you're an employee, perhaps an assembly line worker, and one day you go to your boss and say, "Boss, give me a raise." What's the boss going to say? He'll say, "Why? What for? No, I'm not going to give you a raise. You are doing the agreed upon work for the agreed upon pay. Why should I pay you more?" Then perhaps you might give him some sad story, like how you can't make your mortgage payments, car payment, credit card payments or whatever. To that he'll reply "What is that to me? I'm running a business here. Now get back to work." And so on.
That's the illustration of the unprofitable servant who only does what he is told. He gets nowhere beyond where he is.
But when you think about it, the employee in my illustration has got no different equipment than his boss, or the president of the company, or any rich or powerful person. He's got a functioning body, a functioning brain, and there is no fundamental reason why he can't be more than he is, if he stops begging for a hand-out and takes some initiative.
So, first is the "mustard seed" part. "If you have faith as a mustard seed..." means you've already got what it takes and don't need anything more. We know that the mustard seed is this tiny thing (about a half a millimeter in diameter, like the size of a poppy seed), which can grow into this huge, tree-size plant that birds can nest on. Everything it needs is there. But then it has to die (first faith risk, be buried). Then it steps out by pushing out roots (another faith risk), sprouting above the ground (another faith risk), and so on, each time getting more nutrients that it needs to grow more. It becomes more than a little seed, something much more glorious and useful.
More importantly, the "mustard seed" inherently "knows" how to become a tree-size plant. It's been designed that way.
So all of us have the ability. We've already got it. We already have what we need.
Back to the assembly line worker, if he puts his mind to it, and takes the initiative, maybe investing some extra hours figuring out how to make his line more efficient, or whatever, then when he is successful at contributing more, his boss will put him in charge of that line, and give him a raise, because he is more valuable to the company. Then he uses his new position to take a greater initiative, gets more responsibility, then gets another raise, and so on.
The end of Jesus' illustration is "we are unprofitable servants, for we have only done that which we were obligated to do."
So this comes back to the point of where we started. You can "want to be" something all day long and day after day, you can sit and wait for God to give you explicit direction through special revelation, go to lots of conferences and seminars, read lots of books, listen to lots of CDs, or perhaps just read the scriptures over and over again and do the minimum spelled out there that you need to get by, all well within your comfort zone. If you do that, you are the "unprofitable servant" and will just get your basic needs met, like a slave.
Rather, you must decide to step out in faith, and do it. Once you step out in faith, you will get results to the extent you stepped out to further the Kingdom of God (your boss). And then you will immediately realize that you have more faith, because you just stepped out and got results! So you step out again, and again, in bigger and bigger ways, and get bigger and bigger results. But if you just sit and mull over the truths of God and the possibilities, then you will get nowhere.
The text uses the Greek word "doulos" (slave, bond-servant) not "diakonos" (servant, more generally). You don't want to act like a "slave," because slaves are just told what to do and do what they are told. We are sons and have the privilege of stepping out in faith and expecting results, with the backing of our Father in heaven.
Being a slave requires no faith. You just wait for someone to tell you what to do, and you do it. In fact, a slave will obey to the letter of instruction to avoid punishment.
Remember the Gal 4 illustration of Hagar and Sarah. We are sons of the promise (the free woman), not sons of bondage (the slave woman). Just "doing what you are told" is an "under the law" slave mentality. So we are back to the same issue of "law" (bondage) vs. "faith" (freedom).
Most of popular Christianity has a slave mentality. They say "Lord, increase our faith!" Then they just wait to do what they are told, and then somehow expect to get rewarded with more "faith." You see how Jesus closed his illustration by insulting his disciples for asking the question in the first place. And he didn't give them what they wanted (more "faith," just for the asking, as if he could magically impart "believing" to them).
In my illustration, the assembly line worker needs to take a risk, make a personal investment, and step out in faith before he is going to make anything more of himself. His boss isn't going to give him any credit until he does. Even if he stumbles and is unsuccessful at the first try, if he has grit and perseverance, and keeps stepping out in faith, he will eventually be successful.
"Lord, increase our faith!" is a cop out. Hebrews 11:6 says "without faith it is impossible to please God," so faith is our part. Hebrews 11:1 says, "Faith is being sure of what we hope for and certain of what we do not see," and the rest of Heb 11 gives testimony after testimony of what men did in faith. You don't ask God for that. You believe, step out in faith, and do it.
I grant this work to the public domain.