Moral Absolutism is considered, in the religious world to be one of divine law. That is there are commandments of the Lord, and thou shalt follow them or be eternally punished.
In the old Jewish law there were punishments for not obeying the injunctions of Deuteronomy; and there were blessings for following the positive commands.
In modern parlance, today, there is the Catholic Church and Christianity and Islam which have certain Moral Absolutes which MUST be followed or else.
So in that sense of the word, it is a command to obey. No choice, no justification, no way out.
Moral Relativism, is highly dependent. This is the more pragmatic approach, one followed even within the major religions.
The reason is quite simple logic actually. Its simply that though people may do wrong, they may also be forgiven. Therefore, though their reasons for doing what they do are flawed, that is there is a defense such as mistake, there is also a justification for not punishing a moral aberration. That is excuse through forgiveness.
Moral Relativism in its extreme form is the justification of murder "in the name of God". Therefore, Moral Absolutism is an utopian ideal, that is impossible to reach.
Moral Relativism is pragmatic, and can be used to justify just about anything.