Here’s a translation of the verse nine of the Isha Upanishad: “The ones who worship avidya, enter blinding darkness; those who delight in vidya, enter darkness that is even deeper."
Avidya refers to the life of karma (actions which lead to the fulfillment of worldly obligations), while vidya refers to the knowledge that one gains from a study of the scriptures. This verse rejects the dichotomy between avidya and vidya, or between the life of action and the life of wisdom. Avidya is necessary for wisdom; man cannot achieve wisdom until he has attained the worldly experience that comes from the struggle to perform the actions which lead to the fulfillment of worldly obligations—to attain a higher level of existence, he must begin by consummating the duties of the lower levels of his existence. Likewise, vidya is an essential prerequisite for karma—a man lacking in vidya, finds it difficult to make moral choices.
Those who engage solely in actions (work), and pay no attention to intellectual pursuits, enter into darkness. While those who engage solely in intellectual pursuits become detached from reality and are lost in an ersatz world of their own rationalizations—they enter into a greater darkness. Intellectual pursuits are of little value, if man is lacking in the will to take actions which lead to the fulfillment of his worldly obligations. Thus the Isha Upanishad rejects the views of both schools: the school which preaches that good life is intellectual, and the one which preaches that good life is materialistic—and preaches that a good life is a combination of both, intellectual pursuits and materialistic pursuits.