"We are all free only to decide who we will serve."
For example, to "be free" from over-eating, we must become "enslaved" to the constant pressure of dieting. That is why life is so difficult: No matter how free we think we are, we're never 100% free. Which is why I think it's interesting that Jesus talked about "laying down our burden," and said that faith in God makes us "free indeed." The way God makes us free is to "enslave" us entirely to Him. Which, of course, only works if we believe God is a better master than anyone else, including ourselves. Perhaps this is a bit frustrating to us, with our Westernized views of freedom and individual autonomy. But I am more and more convinced that it is the truth.
I feel like I should add this, just as a clarification... the above statements regarding the limitations of free will should not be construed as an argument against existential individuality or subjectivity, both of which I still hold onto as important realities. I am simply trying to describe the finite nature of human freedom. This does not make freedom any less real with regard to the person and to faith.