Another source that really helped me understand the book of Revelations better (notice I said better, not well, because that is such a hard to understand book of the Bible) is a 5 book series on Revelations by Elder Athanasios Mitilinaios. It's basically transcripts of weekly lessons he gave on the topic in the early 80's, as translated by Constantine Zalalas. There's a ton of information in every lesson, and it's applicable to our Christian life now.
You can get them from St. Anthony's Monastery in Arizona.
https://stanthonysmonastery.org/search?q=Revelations+Athanasios+Mitilinaios&options[prefix]=last
There's another little booklet,
A Ray of Light, by Archimandrite Panteleimon of Holy Trinity Monastery in New York, first published in 1946. Another useful book is
The World's Final Call, by Vassilios Bakoyiannis. These focus more on the time of the Antichrist, but it's good to know more about that time as well, so we don't get scared thinking the Antichrist is going to come to power any day now.