"It would be eighteen hours at least before she was in time again" (Huxley 140). Lenina has gone on soma-holiday, which leaves her fast asleep for eighteen hours. Because of her current state, if anything were to happen to her, she wouldn't be aware. This gives John the perfect opportunity to creepily break in and watch her sleep.
Best soma holiday ever!
"How beautiful she was! How beautiful" (Huxley 144). John has basically become this creepy pervert that gushes over how beautiful Lenina is. He gets this undeniable temptation to touch her, which increases the creepiness that is already present. Fortunately, this temptation is resisted as his hand was unworthy of touching her.
OMG it's Lenina. She's soooo beautiful!
"He was ashamed of himself. Pure and vestal modesty" (Huxley 145). Well, John's temptation was unbearable so he ends up touching Lenina. Eventually, his urges take over and out of modesty, he strips Lenina naked. Ashamed of himself, he quickly shuts his eyes. Luckily, Bernard came back in time so that John could escape from the horrid thing he has done.