Darth Avlectus

It really depends on what you mean by self sustaining.

If you are talking about the reason God(the creator/YHWH/$DIETY) chooses not to involve Himself(herself/themselves) with our mundane existance and prefers to allow strife in our lives, it is much the way a mother bird will push their chicks from the nest. As we have free will, God gives us tasks to do so that we may grow. While it may be easier to "miracle" us to better lives, it ultimately lessens our ability to learn and grow. By being self sustaining we are free to discover God in our own way. That discovery is more effective than a simple "Believe in me or else..." method. We see things in different ways and catch the hints at God.