The Buddha did not preach all that he knew from enlightment and practice. On one occasion while the Buddha was passing through a forest hee took a handful of leaves and said: "Dear Bhikkhus, what I have taught is comparable to the leaves in my hand. What I have not taught is comparable to the amount of leaves in the forest." In fact he taught what hee deemed was absolutely essential for one's purification making no distinction between an esoteric and exoteric doctrine. He was characteristically silent on questions irrelevant to his noble mission, such as How big is Universe? Is it finite/infinte? Is it eternal? Buddhism no doubt accords with science, but both should be treated as parallel teachings, since one deals mainly with material truths while the Buddhism confines itself to moral and spiritual truths. The subject matter of each is different. The Dhamma he taught is not merely to be preserved in books, nor is it a subject to be studied from an historical or literary standpoint. On the contrary, it is to be learnt and put into practice in the course of one's daily life, because without practice we cannot appreciate the Truth. The Dhamma is to be studied, and more to be practiced, and above all to be realized; immediate realization is its ultimate goal. As such the Dhamma is compared to a raft which is meant for the sole purpose of escaping from the ocean of birth and death (called Samsara). Buddhism, therefore, cannot strictly be called a mere philosophy because it is not merely the "love of, inducing the search after, wisdom." Buddhism may approximate a philosophy, but it is very much more comprehensive. Philosophy deals mainly with knowledge and is not concerned with practice; whereas Buddhism lays special emphasis on practice and realization.