The Rainbow in the Cloud

This discourse was taught by the Rebbe on Shabbat Sedra Noah in 1982.  After the Flood, G-d tells Noah that He is making a Covenant with humanity that there will not be another total Flood. The rainbow is the sign of this Covenant.  Commentators such as Nachmanides ask: does that mean that there were no rainbows before then? Surely, the rainbow is a natural effect of sunlight in the water-droplets in the cloud?  The Rebbe provides a spiritual way of understanding  a ‘cloud’ and then gives an interesting answer to the question of the commentators.