Spiritual has to do with actual experience, not mere beliefs; with God as the Ground of Being, not a cosmic daddy figure; with awakening to one's true self, not preachy and churchy moralisms about drinking and smoking and sexing; with Spirit found in everyone's heart, not anything done in this or that church….
Meditation is spiritual; prayer is religious. That is, petitionary prayer, in which I ask God to give me a new car, help with my promotion, etc., is religious; it simply wishes to bolster the little ego in its wants and desires. Meditation, on the other hand, seeks to go beyond the ego altogether; it asks nothing from God, real or imagined, but rather offers itself up as a sacrifice toward a greater awareness.
Meditation, then, is not so much a part of this or that particular religion, but rather part of the universal spiritual culture of all of human kind – an effort to bring awareness to bear on all aspects of life. It is, in other words, part of what has been called the perennial philosophy.
Ken Wilber, Grace and Grit, 76.