Know thyself. This means complete honesty with yourself. A spiritual warrior is not afraid of facing any perceived darkness within themselves or the world because they know that this perception can be turned into Light, as it is truly All Light and His Love.
Being honest with yourself means acknowledging that you cannot call yourself spiritual, Christian, Buddhist --- whatever you label as holy --- while you put judgments on others and the world. That is incompatible, as judgment is not of God --- He is Love. Knowing thyself means that you understand that only Oneness exists and what is within you is the same as what is "outside" of you. Thus as you judge others, you are only judging yourself, and your judgment of others is a projection of your self judgment.
If you desire to be a spiritual warrior and fulfill your holiness, to truly help the world, then you must stop laying your perceived sins on the world and heal yourself. When you do this, you become a bright candle that joins others who have lit their candle, creating a Light that dispels the darkness.