Read it through once

It is inquired, for what reason a human being should engage in procuring the happiness, or refrain from producing the pain of another? When a reason is required to prove the necessity of adopting any system of conduct, what is it that the objector demands? He requires proof of that system of conduct being such as will most effectually promote the happiness of mankind. To demonstrate this, is to render a moral reason. Such is the object of virtue.