These two opposites are given to refer to everything concerning Jehoshaphat during his reign as king. Alternate translation: "from the beginning of his reign until he died" (See: [[rc://en/ta/man/jit/figs-merism]])
The word "behold" is used here to add emphasis to the important information that follows. Alternate translation: "anyone can look in the history ... Israel and see that they are written there"