en_tn/psa/089/037.md

It will be established forever

Here "It" stands for David's throne or power to rule as king. This can be stated in active form. Alternate translation: "I will cause it to last forever" (See: rc://en/ta/man/jit/figs-activepassive)

forever like the moon

God compares David's rule as king to the moon to emphasize that someone from David's descendants will always rule as king. (See: rc://en/ta/man/jit/figs-simile)

the moon, the faithful witness in the sky

The moon is spoken of as if it were a person who witnesses God making this promise to David. Alternate translation: "the moon, which is like a faithful witness in the sky" (See: rc://en/ta/man/jit/figs-personification)