It's hard. The symbolism doesn't behave like ordinary drama, and the religious surface can feel closed off even after you've read around it. I didn't get it for a long time but somehow I perservered. Eventually, I got to the point where the music started to carry what the plot withholds: the wound, the compassion that answers it, a redemption that arrives as a change in the sound rather than an argument. I found Scruton's Wagner's Parsifal especially useful here. He treats the religious colouring not as phoney piety but as a coherent drama of guilt and grace, which is why the piece can devastate you before you can say why. Eliot was right that the appreciation can come first. Scruton is one of the better guides to the understanding that follows.