Being dependable and considerate of other people’s feelings
So basically what happened is that the lion - the king of the jungle and a big creature - was annoyed by the little mouse and was about to kill it. However, he saved its life because he thought the mouse was funny and thought that the little critter can't possibly help him in any way in the future. It turns out that he was proven wrong by the mouse when it saved his life when was caught in the trap.
The theme of the story - as seen in the fable - is about not judging immediately. The littlest things in life will unexpectedly have a great impact in the future.
