Rashi explains that this cloud was like a kind of smoke, and Hashem made for Moshe a path in the midst of it.
In Parashas Yisro it states: And Moshe drew near to the thick darkness where Hashem was. (20:18) Rashi explains that Moshe went inside the three divisions: darkness, cloud, and thick darkness. There are three degrees of darkness expressed in the words darkness, cloud, and thick darkness. On this occasion, Moshe was able to penetrate all three layers of darkness, to the very heart of the heavens.
We may apply this image of Moshe ascending to Hashem, as a symbol of overcoming the various spiritual obstacles and crises in one’s life. Similar to one who has spent a good part of his life bound and confined to his material desires and aspirations, and who finally realizes that there is also a spiritual purpose in life. As this individual embarks on the journey of return, many difficulties block his path. Often the greatest difficulties is ingrained habits and attitudes. However, Hashem, in His great love, will give man opportunities to find his way by hiding Himself in these very same obstacles, so that if the individual is resolute, he will find Hashem even in the difficult and complex situations that he faces. In this way, man will ascend through the various layers of mist and darkness which are the symbols of obscurity and camouflage in the physical world. It was through the various types of darkness and obscurities that Moshe had to venture before he could reach the heavens. These mists, as gloomy and forbidding as they may seem, conceal within them Hashem’s pure love for those who are staunch and unwavering in their quest and hope for Him.