There was one vice in particular, a vice which they seem to have adopted from the Asiatic nations of the Persian empire, that resulted in the most awful consequences.

This vice was incest.
The law of God, proclaimed not only in the Scriptures, but in the native instincts of the human soul, forbids intermarriages among those connected by close ties of consanguinity.

The necessity for such a law rests on considerations which can not here be fully explained.

They are considerations, however, which arise from causes inherent in the very nature of man as a social being, and which are of universal, perpetual, and insurmountable force.

To guard his creatures against the deplorable consequences, both physical and moral, which result from the practice of such marriages, the great Author of Nature has implanted in every mind an instinctive sense of their criminality, powerful enough to give effectual warning of the danger, and so universal as to cause a distinct condemnation of them to be recorded in almost every code of written law that has ever been promulgated among mankind.