Heschel was saved from death camps in Germany by a liberal Jewish university in Cincinnati with several other scholars-"College in Exile". Julian Morgenstern, the college president was a life-long friend to Heschel for this, but Heschel did not fit at the university.
So part of my interest in reading this biography is that I knew, from reading his books, that he was a conservative when it came to studying the tradition, treating scripture as sacred, prayer, etc. Yet, I also knew that (unlike conservative christians) he marched with Martin Luther King, even challenged his own followers by saying that King was a living prophet of the Hebrew tradition. I also knew that he invited his daughter to have a Bar Mitsva if she wanted (traditionally for boys); that he was encouraging if she wanted to become a rabbi. I learned that he worked with others, including Berrigan brothers and Neuhaus to protest Vietnam. So I was curious about this person who walked in different spheres.
Here is what I see: A) Human life and humans being in the image of God were of the greatest value. Although Heschel observed many rituals of prayer, food rituals, observing the sabbath and other holy days (even when it conflicted with meeting the Pope, etc though not without exception); he did not value these things over human life. At various times, I remember at a conference on Race where he spoke with other keynotes including Martin Luther King, Jr, he quoted from his tradition that to humiliate another person, because of their great value, is like committing murder. He saw this action all around and stood out against it. B) Although he spent his life accruing a deep, deep knowledge of his tradition, he was comfortable/sought out/ended up conversing and spending time with so many other traditions. I will go further and hazard this--because he felt somewhat out of place in his own tradition (even at the end of his life he couldn't get the administration to move him to an adequate office for his books and manuscripts); because he asked his tradition and his people extremely hard questions (In the only TV interview he says the only people who don't have extremely difficult puzzling questions to grapple with are idiots); he found it easy to converse and meet people outside of his tradition. When he died some of his closest friends were Catholic and Protestant Christians, even someone from Japan who studied under him and wrote about the parallels between Judaism and Buddhism.
So: A) Valued all human life in a deep and real way; B) Comfortable conversing with people of other traditions.
There is a beautiful moment where he speaks at a conference where there are Muslim scholars. Heschel and Seyyed Hossein Nasr were the last to leave and Nasr "took his hand and said, "This is an unforgettable moment for me. I have read everything you have written I could find. God give you strength." Kaplin goes on to say that they had been sitting together at the conference and that Heschel was familiar with Nasr's books on Sufism and Islamic mysticism. "Returning to New York, Heschel shared his enthusiasm for the conference with his students" and asked that his latest book be airmailed to Nsr in Tehran. Then he wrote to Archbishop Appleton saying he hoped to have the book translated into Arabic. AND he found translators and immediately sent $250 check to help pay for it. Heschel was a step closer to his lifelong dream of ultimate reconciliation: "The God of Israel is also the God of Syria, the God of Egypt. The enmity between the nations will turn into friendship."