What is the significance of the social divide between the Eloi and the Morlocks in The Time Machine?

One thing you should be aware of when discussing the Eloi and the Morlocks is that the time traveler himself does not actually understand the full reality of this future world he has landed in. All he has are a series of suppositions, which he amends as he gains more information.
However, across his time in the distant future, he determines that this future age has come into being from the influence of industrialization, as well as from the long-term impacts of those changes on human evolution. His initial assumption is that the Elois represent a humanity that has successfully achieved a kind of utopia, only to devolve as all of those qualities which allowed for civilization's triumph became no longer necessary for survival. Later, he will find this explanation unconvincing, especially after discovering of the Morlocks, which he views as an extension of the working class, just as the Eloi represent an extension of the leisure class. His theories are further amended over the course of the novel, until (towards the end of his time in this future world) he has determined that the Morlocks have emerged as the masters of this future world, with the Eloi in a situation akin to herd animals which the Morlocks pray upon.
Again, it's important to note that all of these suppositions may well be false—the time traveler comes into this future universe from a position of utter ignorance, a fact which he himself is well aware of. Furthermore, consider that his reading of that future is deeply shaped by his perspective as a Victorian. However, if we take his interpretation as our departure point (as I suppose we must, given he is our only source of insight into this future world), what we observe is the final consequences of industrialization. Evolution has worked its power on both the working class and the leisure class, leaving each of them less than human.
Furthermore, note how the Morlocks terrorize the Eloi (representing a reversal of the power dynamics that shape the industrial class structure). If we understand that class structure as inherently exploitative, then we see in their relationship a situation by which the conditions of industrialization has shaped the future of human evolution, with all its brutality and cruelty is now imprinted directly upon the human condition.