I will establish the throne of thy kingdom over Israel for ever, as I promised David thy father, saying: There shall not fail a man of thy race upon the throne of Israel.

then I have established the throne of thy kingdom over Israel, to the age, as I spake unto David thy father, saying, There is not cut off to thee a man from being on the throne of Israel.

Then I will make the seat of your rule over Israel certain for ever, as I gave my word to David your father, saying, You will never be without a man to be king in Israel.

then I will set the throne of your kingdom over Israel forever, just as I promised your father David, saying: 'A man from your stock shall not be taken away from the throne of Israel.'

Then I will establish the throne of thy kingdom upon Israel for ever,.... In a succession in his posterity, until the coming of the Messiah:
as I promised unto David thy father, saying, there shall not fail thee a man upon the throne of Israel; not fail one of his posterity to sit upon it; see 2-Samuel 7:12.

Then - Upon that condition; for my promise to David was conditional.