Well if you want to write an essay about religion, this will be a pretty easy job as long as you take the time to research about this. It’s a vast subject, this world has many religions some even are in complete opposition with each other, so you have to make sure that you gather all the facts before you actually start writing this.

• One god versus many. There are some religions out there that claim there are many numerous gods who can take many forms, while others claim there is only one al mighty God that watches everything and everyone. You have to check for every single one of them and compare them and see the contrast that was created in different cultures around the world. Imagine a Tibetan monk walk and attend a catholic church gathering. This can be quite a shock for him and vice versa.
• Fear vs love. This is the most important topic in my opinion. There are some religions who put the fear of god into people, which contradicts what they say about him because he is all loving and he loves every single one of us, while others teach that we are one with god and our perception if too limited right now to see, or better said, feel that. So make sure that you compare these and you try to see what each and every one of them has to offer.
• Ancient religions. There are some today that have made it through time, but there are numerous religions that have been lost as the years passed by, and some of them pose a very interesting theory about how our world was created and how mankind appeared and why it is as it is today.
• Prophets. Almost every religion has one. This is basically where a religion lays it’s foundation on, a prophet that came to bring the message of god for every one to hear and see. So try to compare the prophets and see if you can find any similarities ( you will find a lot of them ) and to check for differences as well since there are multiple ways to tell a single story, there are multiple ways to present a prophet. This is the best topic if you want to compare Islam and Christianity the two major religions existent today.