Though he had commanded the clouds from above - Though he had showed 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 upon them in such abundance that it might be compared with the waters that had been sent down at the deluge.