John Gill Commentary Psalms 136:9

"The moon and stars to rule by night; For his lovingkindness [endureth] for ever:" — Psalms 136:9 (ASV)

The moon and stars to rule by night
The lesser lights, and which indeed receive all their light from the sun, (Genesis 1:16) ;

for his mercy [endureth] for ever ;
in continuing these lights, so useful to men, as well as in making of them: the moon and stars have their benign influences upon the earth, to produce things out of it useful to men; see (Deuteronomy 33:14) (Job 38:31) ; and are of singular service to benighted travellers, and to those that go down to the sea in ships; see (Acts 27:20) . The moon is an emblem of the church, that receives her light from Christ, the sun, and which will continue for ever; and, stars are emblems of Gospel ministers, who are the means of enlightening dark souls, and of refreshing disconsolate saints; and are a continued mercy to an ignorant world, as well as to the church, and will be continued as long as it stands; see (Song of Solomon 6:10) (Revelation 1:20) (2:1) (Matthew 5:14) (28:20) .