It's now or never. It means that the opportunity is rare and can't be missed.
3, the city gate caught fire, affecting the fish in the pool: metaphor for being implicated and suffering losses or disasters.
4, put down the butcher's knife to become a Buddha: Buddhism believes that everyone has Buddha nature, and the evildoer can abandon evil and become a Buddha. Later, it developed to persuade evil people not to do evil again.
5, near Zhu Zhechi, near the ink is black: red by Zhu, black by ink. Metaphor means that getting close to good people will make you better, and getting close to bad people will make you worse.