Deuteronomy 27:22
Cursed be he that lieth with his sister, the daughter of his father, or the daughter of his mother. And all the people shall say, Amen. Cursed be he that lieth with his sister, the daughter of his father, or the daughter of his mother. And all the people shall say, Amen.
This curse belongs to the directions in Deuteronomy 26 through 28 that state the principles of God's law plainly and practically, teaching that obedience brings blessing and prosperity while disobedience to God's law brings a curse. Its words are the voice of Christ from the enfolding pillar of cloud, expressing the principles of the law of the kingdom of God made specific so that minds are not left in ignorance and uncertainty. It was to be pronounced as one of the curses from Mount Ebal, the mount of curses, upon the disobedient on the day Israel crossed over Jordan, while blessings upon the obedient were pronounced from Mount Gerizim, the mount of blessings. The two prominent mountains were set opposite each other, the one for blessing and the other for cursing.
God showed particular care for forgetful Israel by giving exact directions after they passed over Jordan to plaster stones and write His commandments on them and to repeat the law from the two positions. This was done so the people would hear repeatedly the advantages of obedience and the consequences of disobedience, would have the law impressed upon them, would have it made familiar because of its great importance, and would remember what God required. The people gathered at Ebal and Gerizim to affirm their covenant with God, and after each declaration the whole congregation was to assent to the specifications. Laws and curses including this one were rehearsed before Israel by Joshua, and by accepting the conditions and renewing the obligations before him they placed themselves under solemn responsibility to fulfill them.
The pronouncement was given to deter from transgression and encourage obedience, showing that God takes no pleasure in the death of the wicked but takes greatest pleasure in those who turn from sin. The verse presents the never-ceasing obligation of all whom God has blessed with life and health and advantages in temporal and spiritual things, including gifts, offerings, and the tithe. Its message has not grown weak because of age, and God's claims are just as binding now and just as fresh in importance as His gifts are fresh and continual, with Christ repeating them with His own voice calling His followers to consecration and self-denial.