Why?

Why do we do things? What is our motivation? What makes our society a (usually) low-abiding society? Why do we feel good about being nice to people and helping others?

Simply, because it is Right.
Inherent in each of us is the knowledge of right and wrong. Children understand this concept, especially if they are well-parented. But often we begin to philosophize answers as we ‘mature.’ I’ve noticed in myself that this philosophizing usually is justification for doing what we know is wrong. ‘It’s not that bad,’ or ‘once won’t hurt,’ or you would if you really loved me’ plague our society and warp the minds of our youth. These youth grow up thinking these things and then pass the same twisted morals on (but more on this another time). The point is we make excuses for our poor actions (things we know to be wrong) and believe our justifications are truth.
But truth couldn’t come form man. We are too fallible, we vacillate too much in our beliefs. Not to mention what is ‘acceptable’ to society changes over time (take the media for example). Truth only comes from one source: GOD. He teaches us through scripture and prophets more about what is right and what is wrong. These former abstract concepts become absolute when we realise our Eternal Father gave them to us. They will never change. They are, by definition, perfect.
It is up to us to be humble enough to follow them, to accept them as God’s truth. But it is our choice as individuals. What will you choose? Purpose to life, to be like God by living His truths, or a purposeless life, motivated by the desires and words of those around you?