Herbalism is good practice, in early ages it worked well and did good for many people.

• law of gravity as you mentioned newtons teachings, newton's teachers were researching on force and how it works later on, newton modified it and discovered law of gravity.
• Bible and Quran are both Holy Books from Allah. In Muslims believe, Bible was revealed to Prophet Jesus (PBUH) and Quran to Prophet Muhammad (PBUH), the Bible was variated by the people according to their freedom so Quran was revealed to save the teachings of Bible and also convey new teachings to the people about life.