I usually start my lecture on the subject by saying to the students that I am going to tell them a story that never happened but everything in it is true (from the perspective of the Valentinian Christians that is). I also mention that the main concern of the myth is how this imperfect world of suffering is connected to a transcendent Good God. Or as Valentinus himself said in a letter, how our spirits can come to dwell in this "toilet" (he actually uses language I can't post!).
Then we go on to discover how Plato and Sethian mythology is recombined in a thoroughly Christian context, with the result that our first systematic Christian theology is born. Part of this systematic theology is the use of sacraments, and probably the development of a few additional sacramental practices. What do they do? Nothing less than release and protect the fallen spirit so that it can return home. Marriage as a sacrament is part of this process, and since the Valentinians thought that their own marriages were highly charged sexually in order to conceive children with the strongest spirits, well it is a fun time in class finally getting away from the obscene asceticism of so many of the early currents.