This means he prophesied toward the altar in a loud and condemning voice. Alternate translation: "prophesied loudly toward the altar" (See: [[rc://en/ta/man/jit/figs-idiom]])
The prophet spoke to the altar as if it were a person who could hear him. He said this twice for emphasis. (See: [[rc://en/ta/man/jit/figs-apostrophe]] and [[rc://en/ta/man/jit/figs-personification]])
Here the "family of David" refers to the descendants of David. This can be stated in active form. Alternate translation: "a descendant of David will have a son named Josiah" (See: [[rc://en/ta/man/jit/figs-metonymy]] and [[rc://en/ta/man/jit/figs-activepassive]])