The proof of the essay is in the evidence

Sometimes people ask a deceptively simple question about things. It goes something like this: What is the most important piece of X? What is the most vital organ of the human body? What is the most critical component in a motor car? What is the most important part of an essay?

All such questions have the same answer: It depends! Every piece is important in its own way. You need the engine to drive the car forward but without the nuts on the wheel you can't get the vehicle go very far. Likewise, the brain and the heart matter obviously more than most organs in particular ways, but you need teeth to grind the food and nose hair to filter the dusty air you breathe, and through a complicated chain of relations, the teeth and the nose hair enable the brain and the heart to receive the energy they need to function. 

The same is true for the essay. The thesis of the essay is at the heart of the essay. But unless you feed the essay with concrete and varied evidence, the essay will have no life. 

To repeat, the supporting evidence must at once be specific (e.g. quotations, examples, stories and facts) and diverse (e.g. not all quotes or just stories).