Excerpt on Xenophanes and the Truth Available to Mortals from pages 147-148

The idea that mortals are capable of statements that resemble truth is a very important one, and it is also hinted at in Parmenides' work. Furthermore, this resemblance with truth can be improved by man's continuous efforts, as Xenophanes suggests:

By no means did the gods reveal all things to mortals from the beginning, but in time, by searching, they discover better. 

In other words, the acquisition of knowledge is an ongoing process for human beings as they strive for better and better approximations of truth. If there ever was a statement that presaged the scientific process, it is this one; no wonder it is viewed as tremendously significant by Karl Popper, who focused so much on science and epistemology. The most important thing about searching, then, is not that it provides us with understanding, but that it improves our ability to discover. Thus, "to increasingly approximate truth may very well be a suitable motto for philosophy itself.
As for why the gods refrained from revealing everything to mortals right away, we are not told, nor do we know whether Xenophanes offered an explanation. Regrettably, even fewer fragments of his work have survived than of Parmenides'. Perhaps there are certain religious implications at work here. After all, if mortals knew everything at once, they would be like the gods. Instead they have to work it out, and if all goes well, they find themselves closer and closer to that state—provided, of course, that they have enough time and never stop searching. It seems that the only factor which hinders them from achieving a godlike state is the limit imposed upon their life span.