Microcosm has specific meanings within literature and several domains, but the most relevant to our purposes is its use within early Medieval magic. As Valerie Flint writes in The Rise of Magic in Early Medieval Europe:
...Isidore was a most enthusiastic early medieval propagator of the notion... that the body of a man is a microcosm of the universe and reflects in little all the constituent parts of it. (p. 130)
|Aries by jess (flikr)|
The concept of microcosm had important implications for astrological medicine (a foreign concept to modern ears, to be sure). An illness may be an imbalance of forces within the body brought on by the dominance of a specific star. Healing of some organs may be easier under some constellations than others. The core concept of microcosm is that each individual is connected to the whole universe and reflects that universe -- in ways reflecting a type of sympathetic magic (Sympathetic magic may be worth an exploration on its own in a later post).
Another way to express this notion is in the phrase "as above, so below." Important to alchemical traditions, this phrase emphasizes the parallelism of the cosmic and the personal.
What does this mean for the setting of the Invisible Sun and adventures/stories told within it? The most important implication seems to be that the Path of Suns represents operations at two levels. It refers to a greater geography of planes as well as the parts of an individual character (probably more the character's soul, "essence", or personality than physical parts of her/his body). Moving through the parts of a character's path is parallel to movement through the various worlds.
This may create interesting opportunities for storytelling. If the individual reflects the greater cosmos (and vice versa), a personal story is a cosmic story. A personal imbalance may create a universal imbalance. The destruction of a person reflects the destruction of a cosmos. There are no "small" stories. At the very least, the waxing and waning of the various suns are likely to affect characters in direct and personal ways.
The mechanics may (I just guessing here - I have no more information about the game than anyone else) similarly allow for influences that reflect cosmic and personal influence. A card from the sooth deck may indicate either a development at the personal or the cosmic level. The same card may even have different interpretations at each level -- but reflect a connection between the two.
This view of microcosm has some connection to surrealism as well. A common theme of surrealism is to play with scale -- including elements much larger than they are expected to be (or much smaller), etc.. The use of microcosm in the Path of Suns suggests that our stories can play with scale to a degree difficult in many other games or settings. The game may accommodate both stories of personal discovery and cosmic secrets -- and may let us switch between them.