Well, there's the theme of truth. The characters are constantly seeking the truth about alchemy, their world, and themselves. The military's actions and the secrets they hold also play into this theme. And don't forget the theme of friendship. The relationships between the characters, such as the Elric brothers and their friends, are crucial in their journey through the story.
One of the main themes is the consequence of equivalent exchange. In the story, alchemy operates on this principle, and characters often face the results of trying to bypass or manipulate it. Another theme is the value of human life. The story makes us think about what it really means to be human, especially with the existence of homunculi.
The main themes include sacrifice and redemption. Many characters sacrifice a great deal in their pursuit of various goals, like Edward and Alphonse sacrificing their normal bodies in their failed human transmutation attempt. And throughout the story, they strive for redemption. Also, the theme of family is strong, as seen in the bond between Edward and Alphonse.