en_tn/2ch/21/07.md

the house of David

The word "house" is a metonym for the family that lives in the house. In this case it refers to the kingdom of Judah. See how you translated this in 2 Chronicles 10:19. Alternate translation: "the kingdom of Judah" or "the people of Judah" (See: rc://en/ta/man/jit/figs-metonymy)

he had promised that he would always give a lamp to him and his descendants

Here the word "lamp" is a metaphor, probably for the authority to rule. Alternate translation: "he had promised that David and his descendants would rule Israel forever"