This is the fourth and final claimed prophecy tied to T'hillim / Psalm 89. The psalm laments the fall of "Malchut Bet David," the Davidic royal dynasty. But even has it does so, it reminds us that G-d promised David that the right to the Jewish throne would always remain with David's heirs -- and that this promise is eternal. The psalm emphasizes the guarantee that even if his descendants sin and must be punished, they will not forfeit the right to the monarchy (verses 31-38).
There is nothing in this psalm that speaks of the faithfulness of a human (David or his heirs). It does state that no matter the sins of David or his descendants G-d will remain faithful.
Ergo yet again we have the list maker claiming a "prophecy" that is nothing of the wort.
"If his sons forsake My Torah and do not walk in My judgments, If they profane My statutes and do not keep My commandments, I shall punish their transgression with a rod, and their iniquity with stripes. But I shall not cancel My kindness from him, and I shall not betray My faith. I shall not profane My covenant, neither shall I alter the utterance of My lips. One thing have I sworn by My holiness, that I will not fail David. His seed will be forever and his throne is like the sun before Me. Like the moon, which is established forever, and it is a witness in the sky, eternally true." T'hillim / Psalm 89:31-38.
Revelation 1:5 may say that Jesus is a faithful witness, but "so what"? How many humans are faithful to G-d? Such a claim is not a messianic requirement / prophecy!
The final words of the psalm are "Blessed is the L-rd forever. Amen and Amen." G-d is faithful -- and He will keep His promises to DAvid. It might appear as though our lack of a king for 2600 years is a permanent condition, we are guaranteed of its ultimate restoration and the return of the glorious period of David's monarchy.