It's a timeless and great film for everyone, straightforwardly telling us that life is worth living and a good deed is never lost.
Frank Capra's films always remind me the world is not so bad. He shows us there is no need to beat or convince evil people to change. You will still have people helping you not from a sense of obligation but from a genuine willingness as long as you are kind and honest with them. In such a beautiful world, someone will impress you with their kindness and bring out yours, and vice versa. That's enough, isn't it?