Charles H. Spurgeon on Psalms 104:19

He appointed the moon for seasons. When it is said, that the moon was appointed to distinguish seasons, interpreters agree that this is to be understood of the ordinary and appointed feasts. The Hebrews having been accustomed to compute their months by the moon, this served for regulating their festival days and assemblies both sacred and political. The prophet, I have no doubt, by the figure synecdoche, puts a part for the whole, intimating that the moon not only distinguishes the days from the nights, but likewise marks out the festival days, measures years and months, and, in line, answers many useful purposes, in as much as the distinction of times is taken from her course. John Calvin.