His Holiness the Dalai Lama's book on Heart Sutra is a piece of interesting teaching/analysis for Buddhists and non-Buddhists alike. As THE Dalai Lama, His Holiness on the one hand speaks with classic Buddhist fluency (in method as well as when referring to important Buddhist classics). On the other hand, as a person who has been well connected to and well versed with Western religions and many of their respected leaders, he can communicate well with western audience that consists predominately of Christians
The gist of Heart Sutra is on Essence and Form (The Essence being nothingness but not emptiness).
Some preliminary understanding related to Chapter two is important for a better understanding of the whole book, as I analysed below:
In Chapter two, DL did a comparative analysis of Buddhism vis-à-vis other religions in terms of morality and metaphysics (as well as some practical comparisons, like he said Buddhist monasteries should learn from Christian Chapters to contribute more socially like building schools and hospitals; and that some Christians having been using more meditations in pursue of their spirituality). Basically he said all religions are at one in terms of morality (like he said he agreed with fellow Nobel Peace Prize Winner Archbishop Desmond Tutu that religious leaders should come together to help in time of natural disasters).
Again on Chapter two, on the area of Buddhist's analysis of Essence and Form, he explained that this is the great dividing line between Buddhism and most other religions that believe in the existence of an absolute Being or Beings (normally referred to as God (s)). In the final Buddhist's analysis (of metaphysical in nature), God as an Essence will be analyzed away, i.e. that is no God. As a corollary, DL compared such an in-depth analysis of this fundamental Buddhist concept as like going to graduate school, and shall be attempted only by Buddhists during further pursue of their spirituality. What DL meant is that one cannot BOTH believe in God(s) and believe in the emptiness of Essence (in the final analysis, God as an absolute Essence does not exist), a fundamental conflict of two belief systems.
With the above in perspective, we can understand why the book was organized into three sections. The first section is called Buddhism in Context, give a short comparison on religions (as per above) together with a framework of Buddhist practice and metaphysical system. Putting his Buddhists and non-Buddhists (assuming Christians) readers into different receptive modes.
The second section deals directly with Heart Sutra and is directly relevant to devoted Buddhists. And here DL did a great job in teaching us a comprehensible metaphysical system of Buddhism built upon the Heart Sutra with Essence = Nothingness as its core construct. It is interesting to note that logically (or scientifically) speaking the Heart Sutra is very simple: Behind every Form (including concrete Buddhist practices, as examples of Form), there is its Essence and which is Nothingness (not emptiness). DL also noticed this simple Negation (negation of form and unchanging essence). He explained that this Negation hides the greatest wisdom. But as with all metaphysics, one cannot arrive at a definite proof of one's initial metaphysical propositions. For religions that believe in the existence of absolute Being (or Beings), FAITH fills the missing gap. Buddhism is in an interesting situation, without the authority of a God, a Buddhist has to seek his own Enlightenment. Here, the path to seek a solution for a Buddhist is meditation (assuming that the Buddhist has already practiced Buddhist morality and exercised his logical (conscious) faculty to understand the supporting metaphysical arguments behind). Through deep meditation, a Buddhist can experience by himself (or herself) the meaning of Form, Essence and Nothingness. DL explored the important of meditation in other books of his. Interested readers can refer to How to Practice : The Way to a Meaningful Life.
Look at it from the light of the above, from another perspective of analysis, it seems that the very common Buddhist practice of recitation of the Heart Sutra around the Buddhist world serves as an act of reminder of an important Buddhist teaching (because the Heart Sutra is devoid of metaphysical arguments), though I won't go so far as to say that it is a reaffirmation of one's Buddhist FAITH.
The final section "The way of Bodhisattva", DL teaches that the next step in a Buddhist's spiritual development is to become a Bodhisattva. The Sutra path towards which however has not been discussed in depth here. Needless to say the Tantric path of Deity Yoga will be another story, subject to study or practice to pursue, depending on one's religious affiliation and/or devotion.