It is wrong to murder. Cain knew that before he killed Abel and, therefore, attempted to hide both the corpse and his bloodstained hands. God would have none of it. Lying, stealing, false witness, drunkenness, homosexuality, witchcraft, fornication are wrong. There is never a time when an immoral thing becomes moral - or even acceptable.
Moral law applies to every man, woman and child in the entire universe.
It is stamped upon our members and written in our nature. Creation clearly shows a benevolent and merciful Creator. The order and design of earth, sun, moon, and stars reveal plainly a cause that is systematic and disciplined. The ethical maxims revealed in nature and placed by the Maker in the heart of the creature are laws that cannot be violated without dire and eternal consequences. Violation of moral rules has repercussion in the providential or natural realm.