A young friend of mine from London is visiting Jerusalem. He is the rabbi of a shul there. He asked, "I have someone in my congregation who will only agree to anything if I can show him where it is written in the Torah. He wants to know where it is written in the Torah that it is forbidden to cremate a Jew's body."
I answered, "It says it clearly. The body comes from the earth and it shall return to the earth. You are not allowed to destroy it. It is not even yours. It's on loan until the end of your time here and then it goes back to where it came from."
"But where does it say that you are not allowed to cremate it?"
"I told you, '…you were made from the dust and to the dust you shall return.'"[i] If someone is cremated, their body does not return to dust.
"Tell him that he can't expect to see everything so very clearly spelled out that he doesn't need a footnote to help him. Like the day I did teshuva 40 years ago. I read that we are to take the money for a certain tithe, "bind it" to our hand, and bring it to Jerusalem. I didn't know that the expression 'bind it to your hand' means 'don't spend the money on the way'. So I took a piece of string and I tied the money to my hand and came to Jerusalem!"
Without the Oral Torah, the Talmud, we would not even know what tefillin look like or tzitzis or most of the mitzvahs.
[i] Genesis 3:19 "…until you return to the ground from which you were taken: For you are dust and to the dust you shall return."