If your motivation to do good to others is because of fear of a hell or supernatural punishment, if your motivation is to attain a reward, a post-mortem heaven, or to return to life in a higher caste, you are still unworthy.
The correct reason to do good is simply because it is good. That is the best reason. It is the end unto itself.
But when we help others, when we do good for others-with others, we still are planting a seed that will be harvested later. When we are good to others, whether to people known or unknown, it spreads; especially when combined with the acts and gestures of others. Not every act or gesture and not every time, and not even with every person. Every drop does not raise the level of the creek, but countless drops together do create the flood.
People generally think of a smile as an expression of happiness. A smile can also create happiness. You smile and you feel better. If you are sad, you are slightly less sad. If you are in a bad mood, smiling makes you less cranky. (Try it if you don’t believe!) Doing good works the same way. Do good to others, and you are doing good to yourself. This doesn’t need any supernatural lever to make it true. Sorry, no hocus pocus. Comfort others and you are comforted. Help others and you are helped. Nothing supernatural is necessary.
In the larger sense, the result is that we create a society, a humanity with a higher propensity to be good to one another. That means there is a higher propensity that others are good to you, and if we keep feeding our humanity with goodness then we create a better future for our descendants.
Your only reward is more goodness. Don’t do it and your only punishment is less goodness.
But isn’t that enough?