John Gill Commentary Psalms 78:23

"Yet he commanded the skies above, And opened the doors of heaven;" — Psalms 78:23 (ASV)

Though he had commanded the clouds from above
Which were round about him, his chariots, and the dust of his feet; and which were at his command to go here and there, and carry and let down provisions for his people, as they did:

and opened the doors of heaven ;
as a large granary, from which the manna, afterwards called the corn of heaven, was given out in great abundance, which is signified by opening the doors; see (Malachi 3:10) .