Introduction to Rational Ethics
Morality (any morality): A set of rules for behavior -- "Do this", "Don't do that."
Values: Objects that are necessary for the survival of an organism. (e.g., water, food, ...)
Virtues: Behaviors necessary for obtaining values, according to the nature of the valuer and the nature of the value. (e.g., patience, rationality, persistence, ...)
Ethics: The study of morality.
Part 1: Morality is Fundamental for Survival
All living organisms (including human beings) face one fundamental alternative: life or death. The organism's behavior, its course of action, either leads it towards destruction or survival. Thus, a person's morality is a vital matter.
It can be so in direct ways, such as eating vs not eating, or it can be in less direct ways, such as what foreign policy to adopt in order to avoid war, and which party to vote for in an election, etc.
Part 2: Nature of Emotions
Emotions are psycho-physiological reactions to value judgements. If you judge that a certain value is in danger, the brain automatically initiates a psycho-physiological response that we call the emotion of "fear". On the other hand, if the judgement is that the value has been lost, then the emotion will be sadness.
Note that while the reaction is initiated automatically, the judgement is not – one can change their consideration of what is a value for them or not, and whether the value is in danger or not (such as after a prank reveal), etc.
Thus, nature has endowed us with a biological mechanism to deal with values, either to protect them, try to gain them, or mourn their loss.
The most crucial emotion in this context is that of Happiness. Happiness is the response for achieving a value. Students celebrate their graduation in so far as they regard a degree as a value, and that they have achieved it. People feel happy if they buy a new car, make a new friend, etc.
The second most crucial emotion in this context is Love. Love is recognition of value. In human beings, value depends on virtue: I.e., the value of someone to you (including yourself) is in the ability to obtain values through their choice of behavior. Consider for example a person that is intelligent, good looking, physically healthy, but narcissistic. Such a person is not of much value to others, as they indeed can use such qualities to hurt others. In fact, the better qualities they have, the more dangerous they can be.
Therefore, Love properly should be aimed at a person's virtues, like patience, honesty, kindness, understanding, rationality, etc.
Please here note a special property of Happiness, which is that it is the most self-sufficient of all human experiences. That is, one can say "I want to buy a car so I can go to work", or "I want to eat this burger because it is delicious", but one cannot say "I want to be happy so I can...". Simply, one wants to be happy so one can be happy. We will use this point again later.
Part 3: The Rewards of a Rationally Moral Life
As we have seen, the consequence of a morality is either life or death. However, we have yet to address the question: Why should one seek one or the other?
For the purposes of such an introduction, the answer will be: Because you might want to feel love and happiness, or because you want to feel hate and sadness.
Recall that happiness is the emotion in response to achieving a value, and that values are the basis for life.
Recall also that virtues are necessary for obtaining values, and that love is the proper emotion one should place for virtues in one's self and others.
Therefore, in practicing virtue, one can rationally feel love for one's self, while others can feel love for the virtuous individual. This acts as the motivation required to practice virtue.
Yet, in practicing virtue, and if one is not so unlucky, one will obtain values that will make them happy.
And since happiness is a self-sufficient reward, a reason to seek life instead of death has been established.
Note: Ideas inspired or taken as is from the philosophy of Objectivism. When in doubt, the idea is not mine but that of Objectivism.