doer是什么意思？

The doer of a good deed can feel spiritually rewarded even when they gain no concrete benefits.

I think what Aesop was suggesting is that when you offer a good turn to another human being, one can hope that that good deed will come back and sort of pay a profit to you, the doer of the good deed.

Even if there is no concrete benefit paid in response to your good deed, at the very least, the doer of the good deed has the opportunity to enjoy a kind of spiritually enlightened moment.