I am finding that Michael Singer's book The Untethered Soul is still proving to be a challenge. I mean that in the sense that it is a bit challenging to get through (the writing is a little dense and the concepts deep, although no more so than, say, Eckhart Tolle's writing style), and it's kicking my little spiritual butt.
That aside, I wanted to mention another book Singer wrote back in the 1970s called Three Essays on Universal Law. It is even more dense, stylistically, than his later book, but he also explains the concepts of karma, will, and love in clear ways. It reads a bit like a scientist explaining Eastern concepts. If you'd like to learn more about the laws of karma, how will works, or the law of love, check it out. My advice? Take it slow and in little sections. It will sink in better that way.