show image thumbnail in post preview

I am using the e-wallet theme and I would like to customize it so that the image thumbnail (as you can see in the actual post) shows up on the post preview… my website is primarily for the images and the description is the minor detail so I would like viewers to see the image first above all else.

So any thoughts on how to insert the thumbnail into the post preview on the front page?

https://www.opheliajewellery.com/style