Arguably the investment in a lens will outlast a series of bodies if the history of DSLRs is anything to go by. Bodies change frequently, while lenses not so much. I believe this is mostly because bodies are centred around electronics, and lenses around (electronics of course but) mainly optics - and these change at a much slower rate. Hence one could argue that the decision as to what lens, or for that matter lens system to engage with can have long-reaching effects. So lenses deserve their own space for discussion.
I see a lot of people buy into a camera system because of the bodies. For myself, having shot quite a few brands, when I moved from film to digital, I choose my dominant brand based on the glass rather than the bodies at the time. I have not personally regretted that decision.
Understanding lens concepts such as focal length vs field of view and the impact on how a sensor alters what is delivered by a lens and how we have to then consider that when looking at lens focal lengths (equivalence) are always interesting topics.