Computer is a device to implement logical steps to solve problem. There is nothing mystic about it. Church-Turing thesis came out before computer. In an earlier response to JFF, computation is not just about numeric, but symbolic also. Anything that you can describe, and be represented in language, can be done through computation. That is Church-Turing thesis, you don't have to believe it. It is not provable, but no one has ever come up with an counter example.