Albert Barnes Commentary 1 Kings 11:39

"And I will for this afflict the seed of David, but not for ever." — 1 Kings 11:39 (ASV)

But not forever - David had been distinctly promised that God would never fail his seed, whatever their shortcomings (Psalms 89:28–37). The fulfillment of these promises was seen, partly in the Providence which maintained David’s family in a royal position until Zerubbabel, but mainly in the preservation of his descendants to the time fixed for the coming of Christ, and in the birth of Christ—the Eternal King—from one of David’s descendants.