I got an item called Mom's Pearl and I would like to know what its effects are.
The Mom's Pearl trinket gives a 10% chance that any heart drop will become a soul heart instead. This stacks with the effects of the Mitre.
In the original Binding of Isaac, you could gain an infinite number of soul hearts, even if they were not shown on the health bar. Additionally, they protect you from red heart damage, which means you will have an increased chance of a devil deal at the end of every floor. Devil deals, though not necessarily a guarantee, usually provide very powerful items that can help you win the run you are currently on. Therefore, soul hearts are a very beneficial health item.
Trinkets in general are not meant to change your gameplay heavily. Instead, they are meant to either augment your current gameplay style/build, or simply to provide minor bonuses. Since Mom's Pearl only increases soul heart chances by 10%, it's an average trinket with decent utility. Whether that's actually worth it for you to keep is up to you - and a large part of why the game is so fun. There is no "correct" item build.