Slowlearner
And if the natural law inclines men towards, say, murder, wy doesn’t it incline men towards resting on the Sabbath or restraining from adultery or homosexuality?
It doesn’t incline anyone to commit any crime, much less murder.
**God as the source of morality (EWTN)
Answer by Richard Geraghty on Dec-15-2006: **
God is the source of morality in two ways. The first is as the Creator of man as a creature of reason, which is the same as a creature with a conscience. Thus man has a natural knowledge of the basics of right and wrong. He knows that he should honor God and not create idols, that he should respect his neighbors and not lie, cheat or murder them, that men and women should be faithful to each other in marriage and not mess around with adultery and fornication, that parents should use their authority over their children for the sake of the children and not their own sakes. These are the natural laws which men know because they are human. This does not mean that they follow this knowledge because, having free will, they often spend a great deal of their lives in not following these norms but insist on inventing rules of their own. They know but they do not do and so become blind and stupid, as St. Paul says in his letter to the Romans in chapters one to three.
The natural law and morality
tothesource.org/3_17_2010/3_17_2010_printer.htm
The natural law is the law of human being alone—not other animals, not birds, not rocks, not trees, not planets. The natural law arises from our particular nature. It is natural insofar as it is rooted in our nature, and moral insofar as our nature defines what is good and evil for us.
Well, just what are we? We are rational, moral animals—the only rational, moral animals. We are the one animal that must think even to survive, and the one animal whose actions are not governed by instincts but are judged by standards of good and evil. We don’t consider it cruel not to teach your dog to read, but we think that keeping children from getting an education deprives them of something they should have. We don’t jail rambunctious roosters for forcing themselves on beleaguered hens, but we send men to the slammer for rape.
Our status as the only rational, moral animal is the source of our natural belief that human beings are distinct from other animals. That is the origin of all laws against murder, for the notion of “murder” assumes that killing a human being is fundamentally distinct from killing a chicken, and that the murderer actually had the moral freedom not to kill (otherwise, jailing the man would make as much sense as jailing the knife). Let go of this fundamental assumption, and soon killing anything will be considered murder (as some animal rights activists maintain) and a murderer’s DNA will be the only culprit (as genetic determinists maintain).
This status as rational animal is exactly what is meant by the assumption that human beings are made in the image of God. The Ten Commandments are, in moral substance, not unique to the ancient Jews. As C. S. Lewis noted in his Abolition of Man, the moral commands to honor parents, not murder, not lie, not steal, and so on, are found everywhere. They are found everywhere because they arise from human nature. To ignore them, or manipulate them, can only result in the destruction of human nature, the Abolition of Man.
Dr. Benjamin Wiker
“Take this and eat it, it is my body…” 
This issue you speak of is one of interpretations of Natural Law not existence of Natural Law.