Arcana Coelestia #861
861. Verse 6 And it happened at the end of forty days that Noah opened the window of the ark which he had made. 'It happened at the end of forty days means the duration of the former state, and the beginning of the one that followed. 'Noah opened the window of the ark which he had made' means a further state when the truths of faith appeared to him.
Genesis 1:6-8
6
And God said, Let there be a firmament in the midst of the waters, and let it divide the waters from the waters.
7
And God made the firmament, and divided the waters which were under the firmament from the waters which were above the firmament: and it was so.
8
And God called the firmament Heaven. And the evening and the morning were the second day.