Shesh I haven't done one of these in a while now have I?

Themes are very important to a story if you wish to implement one, it allows for proper engagement with the reader or someone experiencing a story.

Now one might ask these questions, how does one implement a theme into a story, how do we establish a theme without being straight up with it, how do I know if my theme is bad or good. I'll try and explain how I see these things as best as I can.

See, a theme is used to either convey a message and make a story feel consistent, and it can be something as simple as "Good will overcome evil," which is evident in stories like Star Wars with the Jedi and Sith, or something as complex as "What makes us Human" like in the stories of Nier and Nier Automata. Both of these stories have their themes clear with how the characters act, how the story progresses, etc.

Lets pick a simple theme for the start, such as "Work hard and you will succeed."

Now, you can probably think of a story just from hearing that, where an underdog poor lad works his ass off to try and reach the top, while someone who cheated his whole life to be on top gets his life ruined and is humbled. Both of these characters have something to do with the theme, where the poor lad makes it at the top, while the one who took the easy route fell hard. You can try and add complexity to this where some people don't end up in a good position by working hard, or those who cheated still remain at the top, changing the theme of hard work paying off to how unfair a system or life is and can be.

Theme can be direct or metaphorical, where certain characters can be stand ins for what you want to convey, such as "God's son beating the Devil" where a character, Jesus, is sent by a king, God, to go kill the Demon Lord, the Devil, with some symbolism put in there if you want.

But your theme shouldn't take precedence over your story. A theme like "Forgive and Give Chances" is a good surface level theme in theory, but a show like Steven Universe can have horrible reprehensible people who passed the moral boundary, being extremely abusive, shattering thousands of gems, all other life forms being inferior and casually talking about colonizing earth, be treated as just sad people who need another chance despite being horrible people, a theme like that wouldn't work in Batman if it was used to someone like The Joker, a chaotic murderous psychopath.

Think of a theme like this. You have a pretty standard cake ingredient list, and you want to add flavor to it, and you have several choices. You pick Strawberry, now you have a Strawberry cake, but you think you could add a bit more to make it special, adding some red food coloring to make the batter red, add bits of strawberries into the batter, add some frosting, and voila, you have a special strawberry cake, and if you wanted, you could add another fruit or more to make a fruit cake, but dont add too much fruit, or the cake might be lost and you cant tell what the cake was supposed to be, or go so into making a Strawberry cake that you may as well just have a ton of strawberries, and the whole cake is overpowered.

All I can really say is, Themes are important, but don't treat them more importantly than your story.