Alister McGrath, in theology book Reality, has an interesting paragraph in the relationship of mathematics and the mind of God. I believe there is rationality in the world because we have minds created by God who also created the world–so there is a correlation. McGrath writes:
“Mathematics plays a critically important role in both philosophy and theology. even if theologians seem slow a group seems slow to appreciate this. Augustine is one of the relatively small group of theologians who regarded mathematics as having theological significance. while his interest in, for example, the derivation of numbers from the mind is often regarded as a quaint aspect of his ‘Pythagoreonism ‘, it is also an important aspect of his understanding of the correlation between the created order and the mind of the creator. Mathematics enables the order within the world to be identified and seen as an aspect of the harmony within the creation, grounded in the being of God.” (170)
I am not going to argue the question whether God exists; it is obvious that everything did not just fall to together. It is deeply satisfying to realize that we can see the handywork of God in manifold ways in this world, and it is orderly, with systems interacting and interfacing with other systems in harmony and with mutual benefits. Our life depends upon that.