We have to nourish our insight into impermanence every day. If we do, we will live more deeply, we suffer less, and enjoy life much more. Living deeply, we will touch the foundation of reality, nirvana, the world of no-birth and no-death. Touching impermanence deeply, we touch the world beyond permanence and impermanence. We touch the ground of being and see that which we have called being and nonbeing are just notions. Nothing is ever lost. Nothing is ever gained. The Second Dharma Seal is nonself. Nothing has a separate existence or a separate self. Everything has to inter-be with everything else.
Excerpt from "The Heart of the Buddha's Teaching"
Is the bold phrase grammatically correct? And what does it mean?
Would it be better to replace 'which' with 'what'?