This is a book for undergraduates, and it’s a good thing that you didn’t grok much. It’s kind of like an intro chemistry book. If you really want to understand chemistry you need quantum mechanics, but it’s a bad idea to start (most) chemistry students off with Schrodinger’s equation. If you want to grok particle physics you need QFT, which is among the most difficult subjects. If a non-QFT person tells you that they read Griffiths’ particles book and understood it all then they don’t know what it means to understand something.
This is a book for undergraduates, and it’s a good thing that you didn’t grok much. It’s kind of like an intro chemistry book. If you really want to understand chemistry you need quantum mechanics, but it’s a bad idea to start (most) chemistry students off with Schrodinger’s equation. If you want to grok particle physics you need QFT, which is among the most difficult subjects. If a non-QFT person tells you that they read Griffiths’ particles book and understood it all then they don’t know what it means to understand something.