Excerpts from Chapter 1 - What the Buddha Taught, written by Dr. W. Rahula.
The Buddha was not interested in discussing unnecessary metaphysical questions, which are purely speculative and which create imaginary problems. He considered them "wilderness of opinions." However, there were some among his own disciples who did not appreciate this attitude of his. One disciple went to the Lord Buddha and asked him the ten well-known classical questions:
The disciple said: "These problems the Blessed One does not explain to me, I do not appreciate it. If the Blessed One explains them to me, then I will continue to follow the holy life under him. If he does not explain them, I will leave the Order and go away."
The Buddha asked if he ever told the disciple to come and lead the holy life under the Blessed One and the Blessed One would explain these questions. The disciple said NO. The Lord asked if the disciple ever told him he would lead the holy life under the Blessed One, and the Blessed One would explain these questions." The answer is still NO.
The Lord Buddha said: ' Suppose a man is wounded by a poisoned arrow, and his friends and relatives bring him to a surgeon. Suppose the man should then say: " I will not let this arrow be taken out until I know who shot me. I will not let this arrow be taken out until I know the kind of bow with which I was shot; the kind of bowstring used; the type of arrow; what sort of feather was used on the arrow and with what kind of material the point of the arrow was made." That man would die without knowing any of these things. Even so, if anyone says: "I will not follow the holy life under the Blessed One until he answers these questions such as whether the universe is eternal or not, etc., " he would die with these questions unanswered by the Tathagata.'
Of what I have known, I have told you only a little, what I have not told you is very much more. And why have I not told you? Because that is not useful..not leading to Nirvana. That is why I have not told you those things.
Then what have I explained? I have explained dukkha, the arising of dukkha, the cessation of dukkha, and the way leading to the cessation of dukkha.
Why have I explained them? Because it is useful, is fundamentally connected with the spiritual holy life, is conducive to aversion, detachment, cessation, tranquillity, deep penetration, full realisation, Nirvana. Therefore I have explained them.