We have seen a lot of numbers repeated lately: 7, 4, 24, etc.
I have compiled a list of website commentary for you all to better understand the symbolism here. Just keep in mind not all numbers have symbols behind them and are just numbers.
This site goes over the numbers with the perspective of what it meant to the first century believers. Excellent for us since they mean different things today. http://www.granbychurchofchrist.org/Bible/KingJames/Revelation/StudyGuide/NumericalSymbolismInRevelation.htm
This site has a great explanation of the number 7 (which scholars think came from 3–Triune God + 4–Creation). Never knew that before!
Guide to the number 1000 and 144,000:
Useful, concise, and short guide to numbers and Revelation in general:
Finally, an in-depth review of all numbers in the entire Bible. Very lengthy but goes through the numbers one by one and lists tons of Bible passages. Easy to scroll through and find the number you want to know more about:
Hope this helps!!