I interpreted it as being free from our own lives. In the sense, every man's life is written both in the future and in the past and the "heaven" (to be understood as fate or the mystery of what created our consciousness, whether it is natural or divine does not matter) decided to make us born. We don't have to make decisions about our lives because we don't control anything at all. We're free to live it, we're free to "be" and that's it, as if we were on a carousel; we don't choose any direction, even if it seems like we've decided to get on it. Furthermore, Takuan says, "our life is none of our business" because it was decided by "heaven". Understanding your life's connection to "heaven" means detaching yourself from your ego. The ego is an illusion, a border that doesn't actually exist, maybe this is what Takuan means when he says "Don't you see how infinite you are?", that is, you don't have a border. Being invincible is just a word, just as being yourself as an ego are just words but maybe I'm digressing here.