It signifies the idea of beginning; round number counting always begins with one. In order to have arrived at whatever age I am at the present moment, I first got to one. The seconds and days and years added themselves on -- but always one at a time, despite the seeming quickness or slowness of some seasons.
It signifies unity; within a person as well as with others. You don't have to be diagnosed with DID to be prone to disagreement with yourself. If you don't believe me, see what happens in your head the next time you reach for salty high-carb snacks that don't go with your diet; or when you need to decide whether to get out of bed for your daily run on a particularly drizzly day when your quilt is being very affectionate. For me, "one" is a reminder that I no longer fight myself over whether to go to work, whether to eat, whether I am bookish and analytical or creative and unstructured. I have found that it's absolutely possible, absolutely livable, to be bookish and creative and analytical and unstructured. Once I ceased to see the elements of my life as mutually exclusive, it became possible to live with them all, and that's such a relief because it doesn't feel nice to be rejected -- if only by yourself.
Finally, "one" signifies my Creator, the one without whom I wouldn't have made it through these nearly 31 years, let alone written 31 daily posts about them. I wouldn't say that faith is a huge part of my life; it is my life. It's a faith that has grown quite separate of my earlier experiences, mostly for the better; a faith that I have sought and asked for and wrestled with in order that it could become every bit my own. And what is faith without an object? Mine is utterly in God, who is one. Not "one of" a pantheon of guardian deities; just one. Not "one among" equals. One. Only. So massive that I can never coax my mind into understanding Him; so good that I can never stop wanting to.