en_tn_condensed/2ch/07/18.md

I will establish the throne of your kingdom

Here the throne represents ruling. Establishing the throne of Solomon's kingdom represents causing Solomon to have descendants who will rule over Israel. Alternate translation: "I will make descendants of yours rule over your kingdom" (See: rc://en/ta/man/jit/figs-metonymy)

A descendant of yours will never fail to be ruler in Israel

This can be stated positively. Alternate translation: "One of your descendants will always be ruler in Israel" or "Descendants of yours will always rule in Israel"