Albert Barnes 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 - Though he had shown that he had absolute control over the clouds, and had only to command them and they would furnish rain in abundance. Compare the notes at Isaiah 5:6.

And opened the doors of heaven - As he had done at the deluge (Genesis 7:11). The idea is, that he had rained down manna on them in such abundance that it might be compared with the waters that had been sent down at the deluge.