A religious text is considered to be the line in the sand.
The text is a persons interpretation of something
Quite a few religions out there. I wonder if they all state the same. If not; why is one supposedly the "source" or absolute?
It is as good a line in the sand as any other choice, and far better than most.
Many people here believe in relativism. They believe morals are based entirely on the individual. If that was the case, then murder would not be wrong if the person who committed it did not think it was wrong. Since murder is universally reviled as wrong, we can show that there are some absolutes in morality.
If there are some, then all can be as well. The only way to ensure you are excluding all morals from being absolute is to say none of them are absolute, and we already showed this to not be true.