Within the framework of the Buddhist Path, reflecting on suffering has tremendous importance because -realizing the nature of suffering, you will develop greater resolve to put an end to the causes of suffering and the unwholesome deeds which lead to suffering. And it will increase your enthusiasm for engaging in the wholesome actions and deeds which lead to happiness and joy.
Whether you believe in God or not does not matter much, whether you believe in Buddha or not does not matter so much; as a Buddhist, whether you believe in reincarnation or not does not matter so much. You must lead a good life.
I believe all religions pursue the same goals, that of cultivating human goodness and bringing happiness to all human beings. Though the means might appear different the ends are the same.
Misunderstanding may arise by confusing the Buddhist and scientific definitions of death. Within the scientific system you spoke quite validly of the death of the brain and the death of heart. Different parts of the body can die separately. However, in the Buddhist system, the word death is not used in that way. You'd never speak of the death of a particular part of the body, but rather of the death of an entire person. When people say that a certain person died, we don't ask, "Well, which part died?"
We are all here on this planet, as it were, as tourists. None of us can live here forever. The longest we might live is a hundred years. So while we are here we should try to have a good heart and to make something positive and useful of our lives. Whether we live just a few years or a whole century, it would be truly regrettable and sad if we were to spend that time aggravating the problems that afflict other people, animals, and the environment. The most important things is to be a good human being.