Try experiments on my rats

I just want to repeat a portion of the C.S. Lewis quote below. I think it needs repeating:

“Novelty may fix our attention not even on the service but on the celebrant. You know what I mean. Try as one may to exclude the question, ‘What on earth is he up to now?’ will intrude. It lays one’s devotion waste. There is really some excuse for the man who said, ‘I wish they’d remember that the charge to Peter was Feed my sheep; not Try experiments on my rats, or even, Teach my performing dogs new tricks.”