They say past is prologue, and when it comes to Bless Me, Ultima, they're not wrong (whoever they are). Antonio's future is at first defined by the pasts of his parents, but as he comes of age throughout the novel, he learns to forge ahead with what he's learned to create a new future that's colored by the past, but not defined by it. In that sense, the novel shows us that while we should cherish and value what's come before, we should never be afraid to make it new.
From Ultima, his father, and mother, Antonio learns that he will always be tied to his past. But it's the whole not-letting-the-past-dominate-his-every-decision thing that allows him to grow into a man and start to forge his own future.
At times, Anaya uses the past to serve as social commentary. It isn't an accident that the subjects of railroads and barbed wire come up more than once. The past event of closing the West is seen as a fracturing and near destruction of past cultures.