This truly ancient book (third book in the Old Testament) dates from around 1400 BCE with parts to perhaps as late as the 3rd Century BCE.
Interesting as a historical collection of documents, it reflects the needs of the then-nomadic Tribes as they wandered the Levant.
Certainly of historic interest, but relevancy to our modern world is perhaps questionable. Anyone can reach back into the distant past to find quotations that serve their own interests. I am certainly not denigrating the value of these ancient beliefs, but we have advanced considerably in our systems of government, our knowledge of science, human sexuality, etc.
Killing people who are different than ourselves is simply not excusable, and that goes both ways. What the shooter did is inexcusable, as is excusing hatreds via ancient texts. What was "wisdom" thousands of years ago is, of course, interesting, but we have progressed far beyond those ancient hatreds, haven't we?