Meaning of Chapter 10 Verse 94

I have done a lot of research on this verse, on the internet, but still haven't found a pleasurable response. The verse states: **"So if you are in doubt as to what We have revealed unto you, then ask those who read the book (sent) before you. The Truth hath indeed come to you from your Lord, so be not of the doubters.”** 2 question comes in my mind when looking at this verse: 1. Why exactly does Allah mention the doubt in our prophet mind? 2. What exactly does it mean when Allah says "ask those who read the book (sent) before you"...as in ask the people of the gospel or the Torah? I hope you can clarify this verse for me so that it eliminates some doubts in my mind. If there's a better, English VERSION, of the tafsir if anyone finds can please link it in the comments below. Jazakallahu Khair.