To "get it", you must start asking yourself certain questions.
It is greater still in the case of several corresponding changes.
What is "it"? We know it is "greater". What has already been said to be greater, in the part you've understood?
Which changes are we talking about? What does it mean when several changes correspond?
But it probably reaches its highest point in the case of the empirical sciences
What reaches its highest point? Is it the same "it" that was greater, greater still, and now highest, i.e. greatest?
Why "empirical sciences"? Are there sciences that are not empirical? How about history, mathematics, economics?