Isaiah 23

As Isaiah writes, what I see as is last "burden of" of foreign nations, he prophecies concerning Tyre, one of the most prosperous seaports in Isaiah's day.  Obvious, with all their wealth, this city also was wicked of which Isaiah prophecies -

"Who hath taken this counsel against Tyre, the crowning city, whose merchants are princes, whose traffickers are the honourable of the earth?
9 The LORD of hosts hath purposed it, to stain the pride of all glory, and to bring into contempt all the honourable of the earth."  (Old Testament | Isaiah 23:8 - 9)

In all their arrogance, it was the Lord that would "purpose" their demise and humility.  And in their demise and humility -

" it shall come to pass in that day, that Tyre shall be forgotten seventy years, according to the days of one king..."  (Old Testament | Isaiah 23:15)

And then -

"...after the end of seventy years shall Tyre sing as an harlot.
16 Take an harp, go about the city, thou harlot that hast been forgotten; make sweet melody, sing many songs, that thou mayest be remembered.
17 ¶ And it shall come to pass after the end of seventy years, that the LORD will visit Tyre, and she shall turn to her hire, and shall commit fornication with all the kingdoms of the world upon the face of the earth."  (Old Testament | Isaiah 23:15 - 17)
I have no idea why this people would be taught humility and then return to commit all manner of wickedness.  Maybe it was so those in the latter days would see the fulfillment of one of Isaiah's prophecies.  We do know the Assyrians came in and destroyed Tyre fulfilling the prophecy.