Renku is a spiritual exercise. The Japanese Buddhist poet-monks who designed its rules understood it as a ritual through which people can examine this universe closely, stretching and sharing their imaginations, to help each other realize, together, how temporary all things are. For Buddhists, this is a step toward enlightenment. Stop clinging to things and people, Gautama Buddha taught, because clinging leads to suffering.
Let me hasten to add: Buddha advises us not to cling; he never says, "Don't love!" In fact, Buddha's compassion is infinite and unfathomable, say the Buddhists.
Other religious traditions teach a similar lesson. Followers of Jesus, for example, are told to let go of their old lives, their old obsessions: drop everything on the road, especially their own self-serving ego-baggage ... and follow HIM.
Renku is sneaky. It's a fun little language game that you can play with friends, but before you know it, you start realizing how healing it is, how sane it is: to let go of your selfish obsessions for just a minute to explore, with friends, this thing called life.