Get an orbital sander with 60 or 80 and 120 grit sandpaper. Sand over the edges, smooth out any imperfections and round corners with the 60/80 then give it a good once over with 120. Afterwards, come back with a dark stain or some dark danish oil. If using the danish oil you're done, if staining then you'll need a protective coat.
Cheap orbit sander (can spend more or less, though I have this one and it works great),
https://www.amazon.com/gp/product/B00OJWLZMW/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
60 grit sand paper (I like 80, but didn't see that in stock. I personally keep both 60 and 80 on hand)
120 grit
Danish oil
https://www.lowes.com/pd/Rust-Oleum-Brown-Danish-Oil-Actual-Net-Contents-16-fl-oz/1000535835
Do what I suggested above and you'll take it to the next level and be very happy with the results!
**An orbit sander is easy to use though I'd practice on a piece of scrap before working on the shelf.