Belief in karma is considered the beginning of wisdom in Buddhism. It is not the end of wisdom. That is, belief is karma, acceptance and understanding of the law of Karma, is only one of the teaching of the Buddha. Chapter 13 of An Open Heart brings us to the highest teaching within Buddhism. Hence, the Dalai Lama calls this chapter "Wisdom" and does not even mention karma within the chapter.
Karma or the law of karma is a fact that should be acknowledge as a truth of the world. Belief in karma, is one element of what the Buddhist path is called Right Thought or Understanding. If acknowledged, karma or belief in karma, helps one act virtuously, and furthermore, helps one accept calmly the events that befall us--good and bad--in this life. Belief in karma helps Buddhist develop the virtuous living, which is an element of the Path to Nirvana or true happiness. Belief in karma can be seen as a step towards the goal. The goal is Nirvana, a supernatural state of being that includes moral virtues, like patience and compassion.
Therefore, it would be misleading to characterize Nirvana as a state of being that results from an individual striving for good karma. If a Buddhist strives to do good or act virtuously in order to achieve his/her own Nirvana, then what is the motive of the Buddhist, other than his/her selfish desire for Nirvana? Such a pursuit of ultimate happiness (Nirvana) would contradict another teaching of the Buddha that says that selfish pursuit of goals creates sorrow or unhappiness (called dukkha)!! Buddhism solution: pursuit of good actions with an eye towards reward in this life and the next, does result in good karma but NOT Nirvana. Such good karma results in a better earthly rebirth eventually. However, if a person achieves the wisdom that the Dalai Lama is about the explain within this chapter, he/she will not cease to do good and accumulate good karma or merit. According to Buddhism, one can reach a state of spiritual development in which one has accumulated great amounts of karma, but that one uses the energy of such karma to help others and in some cases, to actually give good karma to others. Most Buddhists would say that this is a rare event, since in a given lifetime, few, if any persons, achieve this advance state called the bodhisattva level of spiritual practice. No doubt that the first Buddhist to hear the Gospels, and the stories of Jesus healing the sick, thought of Jesus in terms of the Buddhist concept of a bodhisattva, who out of compassion, and selflessness, gave his karma to the faithful.
What is Nirvana? According to some Buddhist, it is a state of mind and state of being that contrast to our ordinary states full of change, anxiety, ups and downs, and lack of mind control. Our ordinary state of mind/being is referred to as Dukkha or sorrowful and/or never fully satisfying. Once we achieve this state of mind/being called Nirvana, upon death of the body, we passed to a disembodied state of Pari-Nirvana. It is a state of perfect, non-changing peace that can not be described, but only experienced. Pari-Nirvana contrasts with samsara, the cycle of being born again and again as govern by the law of karma. For once Nirvana is reached, and upon death of this body, Pari-Nirvana, the person is not reborn again.