Since the sun's light represents the Lord's Divine Truth, “shade” represents a spiritual state in which that light is partly blocked. The theological works of Swedenborg often use the word “obscurity” for this -- a state in ideas about the Lord and life can only be understood in a vague and general way, with little in the way of color or detail. It's also interesting to note that if you're in the sunlight, a shaded area appears very dark, and it may be impossible to see objects in that shade. That's what the light of hell is like -- a dim light to people who live there, but complete darkness when viewed in the light of heaven.

In the opposite sense, shade can represent protection from the glare of falsity.

'The shadow is good' of the oak, poplar and elm, means complacency.