Ignorance is the root which conditions the mind, distorting our perception, thoughts and views.
We ignore the emptiness of the khandhas, and assign a permanent, fixed self to "our" actions, thoughts and words. The ignorant mind creates the idea of a doer, a perceiver, a knower, which is independent and in control of the khandhas. We see the world as something which can be controlled and possessed by that self.
We ignore the impermanence of conditioned phenomena, and we cling to things, feelings and events, wrongly assuming that they will last forever.
We ignore that happiness and suffering do not come from outside, but it is the mind which creates the internal conditions for those states, according to its past habits and tendencies, and to its past kamma. We ignore the fact that all conditioned phenomena are unsatisfactory at last, and that, because of their impermanence, the satisfaction they bring will eventually come to an end.
We ignore that there is a escape to suffering, and a alternative a unstable, conditioned happiness. We ignore the possibility of Nibbana.
We ignore, in sum, our ignorance, which perpetuates the wandering through life.
The mind does not know these things, and as a result, it grasps the world from a illusory perspective, not seeing things as they are.
Ignorance (not merely intellectual, but also experiential, internalized) is the spark which ignites the flame of craving and aversion.
Understanding the roots and causes of suffering, you eradicate both, the seeds of ignorance and craving.