Any adequate explanation of morality has to account for the existence of moral obligation.
The reason why is because moral obligation is a certain binding of the will to choose good and avoid evil.
It is because of moral obligation that humans are bound to do good things and avoid doing evil acts.
So if there were no moral obligation, anyone could do whatever they want, without blame. Nobody would be obligated to be good.
But if God does not exist, can there be such a thing as moral obligation?
Sometimes the question is stated this way:
If there is no God, who then determines what is right and what is wrong? Who says what you should do and ought not to do.
My friend Peter Kreeft, author, debater, and professor of philosophy at Boston College, has just produced this very well done video that talks about the necessary connection between God and morality.
In other words, this is the moral argument for the existence of God.
Many arguments for the existence of God, start with a certain effect in the world and then reason back to some notion of God as the only adequate explanation for that effect.
The moral argument follows this same approach.
From the existence of moral good and evil, we can infer there must be a supreme “lawgiver” of sorts.