If you ask people for their recommended reading on agile, you'll probably get a list of books on agile process, blogs by agile experts, and social media recommendations to follow that will be full of agile coaches. And, I wouldn't discourage you from reading any of them. In fact, I should probably read a few more myself. But, agile is rooted in good leadership. So, for me, the starting point for any agile reading is understanding how to create better leaders.