Karl Popper is a great believer in the power and virtue of science. And much of the reason that he believes in science so firmly - as we see in both of his essays "On the Theory of the Objective Mind" and "Epistemology Without a Knowing Subject" is that science is falsifiable. It is this aspect of science that - more than anything else - sets it apart from religion and other forms of philosophy. The scientific method, and scientific ways of thinking, allow us to determine whether something is objectively true or not because science provides us with ways of demonstrating that something is false. This stands in direct contrast with an epistemological system such as religion in which there is no way (for example) to prove or disprove the existence of God. Religion, and some philosophy (along with other forms of human endeavor such as art) rely on faith. Science does not, and it is because of this that Popper champions it.
Popper argues for the importance of science in a way that is almost joyous, that compares with the joy that other people take in religious faith. Science to him has a beauty to it in how it allows humans to expand their minds. Because science - and this is one of his major points in "On the Theory of the Objective Mind" - allows us to compare different theories and by doing so come to better, more accurate, and more complete understanding of our world, science is capable of improving the human species. (This argument too is used by people of faith - although they of course argue that it is faith and religion that allow them to improve themselves.)
Popper was arguing against an inductive model of science - that model that required a scientist to intuit which theory came closest to explaining the truth of the world. Science is not necessarily and perhaps not even often the work of genius (in the way that art tends to be) he argued. Rather, science evolves (and takes us as a race with it) by careful and detailed inqui...