Mary will bear "a son" who will be called "the Son of the Most High." Jesus is therefore a human son born of a human mother, and he is also the Son of God. These terms should be translated very carefully.
The throne represents the king's authority to rule. Alternate translation: "give him authority to rule as king as his ancestor David did" (See: [[rc://en/ta/man/jit/figs-metonymy]])