According to Osho, 'poor in spirit' means inner emptiness (shunya): being a nobody, having no claims or self-image—not even the vanity of humility. When the ego is gone, even humbleness vanishes. In this egolessness one realizes, 'The whole is, I am not.' Paradoxically, this emptiness becomes fullness—the richest state, a rebirth into life without ego.
It means dropping your ‘me and mine’ so completely that you feel like nobody—and then you discover you belong to everything.