It’s for YOUR benefit, not his
You seem to lack basic understanding about credit report and scores. You father can’t benefit from your credit. No one can benefit from another person’s credit.
Your credit score has absolutely no effect on your dad’s score, and vise versa.
The ONLY thing you can benefit from is the history of payments that your father will make on this credit card. Payment history builds credit, and adding you as an authorized user will cause this credit card to appear on YOUR credit report, as well as on that of your father’s.
With time, this history of (presumably) timely payments will build good credit for you and raise your score.
Your father had only good intention doing this. He himself has nothing to gain from it.
As to the differences in your credit score, I assume that your father had past problems that lower his score, while you don’t. This is why your score is higher than his.
There is only one downside to authorized user. If your father keeps the card in good standing – great. On the other hand, if he runs into problems and start making late payments (or worse than this – completely default), this will ruin your credit.
If you don’t trust you father, ask him to be removed from authorized user. In any case, after two or three years you should have good enough credit to apply for your own credit card, and then you should remove yourself from authorized user.
Remember to do this in writing, return receipt, and keep the records forever.