Why do I call Myself Spirit?

I made the choice that God is love and so am I.

From the Course in Miracles text 31.IV.1: "You see the flesh or recognize the spirit. There is no compromise between the two. If one is real the other must be false, for what is real denies its opposite. There is no choice in vision but this one. What you decide in this determines all you see and think is real and hold as true. On this one choice does all your world depend, for here have you established what you are, as flesh or spirit in your own belief. If you choose flesh, you never will escape the body as your own reality, for you have chosen that you want it so. But choose the spirit, and all Heaven bends to touch your eyes and bless your holy sight, that you may see the world of flesh no more except to heal and comfort and to bless."

So I let go of the world by saying: "I do not know the thing I am, and therefore do not know what I am doing, where I am, or how to look upon the world or on myself."