כְּ֭יָרֵחַ יִכּ֣וֹן עוֹלָ֑ם וְעֵ֥ד בַּ֝שַּׁ֗חַק נֶאֱמָ֥ן סֶֽלָה׃
It shall be established for ever as the moon; And be stedfast as the witness in sky.' Selah
Rashi on Psalms
and it is a witness in the sky, true The moon and the sun are witnesses to him that as long as they exist, his kingdom will exist, as it is written (Jer. 33:20f.): “If you break My covenant with the day and My covenant with the night, etc. Also My covenant with David will be broken.”