It means with all the seemingly endless vicissitudes of life (and history), the underlying big picture is never changing.  So the more changes one sees in life, the more we appreciate this profound sameness.

As we grow up, for example, we discover more things in the world and its history.  For instance, we get to know how many wars there have been, and become bleeding heart compassionate about all the sufferings they entail. We wonder why, just why there have to be wars.  We have more of such emotional reactions to many other things as we carry on.

But then as we get more mature, we also get to know the inescapable realities of this world. For example, the fact that we exist at all means we need a space for ourselves, at a minimum the space our body occupies, but realistically much more because we need a house to live in, places we can go have fun, etc. If someone encroaches into this space, there is no choice but to fight and kick them out, because it is indispensable to our survival.  A tribe, nation, or a state needs the same space and other resources for existence, and this planet only has a fixed amount of them.  Viewed in this light, wars are then only a very natural part of existence - this world is bound to have wars, as long as the population grows. So this concept of war which was disconcerting at first has become passe because we have matured and experienced more of the reality over time.  

That is, after seeing seemingly endless things happen, we come around to the idea that all those things that appeared to be such a big deal is nothing but a mundane reality, and deep down it is always the same.  In other words, depending on your perspective, nothing stays the same except change, or everything remains the same.