'Law' in the Bible

And his daughter in law, Phinehas' wife, was with child, near to be delivered: and when she heard the tidings that the ark of God was taken, and that her father in law and her husband were dead, she bowed herself and travailed; for her pains came upon her.

And she named the child Ichabod, saying, The glory is departed from Israel: because the ark of God was taken, and because of her father in law and her husband.

And David said unto Saul, Who am I? and what is my life, or my father's family in Israel, that I should be son in law to the king?

And Saul said, I will give him her, that she may be a snare to him, and that the hand of the Philistines may be against him. Wherefore Saul said to David, Thou shalt this day be my son in law in the one of the twain.

And Saul commanded his servants, saying, Commune with David secretly, and say, Behold, the king hath delight in thee, and all his servants love thee: now therefore be the king's son in law.

And Saul's servants spake those words in the ears of David. And David said, Seemeth it to you a light thing to be a king's son in law, seeing that I am a poor man, and lightly esteemed?

And when his servants told David these words, it pleased David well to be the king's son in law: and the days were not expired.

Wherefore David arose and went, he and his men, and slew of the Philistines two hundred men; and David brought their foreskins, and they gave them in full tale to the king, that he might be the king's son in law. And Saul gave him Michal his daughter to wife.

Then Ahimelech answered the king, and said, And who is so faithful among all thy servants as David, which is the king's son in law, and goeth at thy bidding, and is honourable in thine house?

And it has been so from that day forward. David established this policy as a law and an ordinance for Israel and it continues to this very day.