to straighten up one’s life; to correct one’s affairs; to organize one’s finances
—Before asking anyone to marry you, you’ll need to quit playing around and put your house in order.

When King Hezekiah of Judah became ill, he was visited by Isaiah:

In those days Hezekiah was stricken with a terminal illness [sick unto death—KJV]. The prophet Isaiah son of Amoz visited him and told him, “This is what the Lord says, ‘Give your household instructions [set your house in order—KJV], for you are about to die; you will not get well.’” (2 Kings 20:1)

Upon hearing this news, Hezekiah pleaded for his life. The Lord heard his prayers, healed him, and extended his life for another 15 years.

For Hezekiah, house represented his possessions and the royal family. Currently, putting one’s house in order more often refers to the way a person handles his life or how a government or organization handles its internal affairs.

In this verse sick unto death means “deathly ill.” Today we have the phrase sick to death (of), meaning “to be extremely frustrated or bored” about something.