Two quotes from The Isa Upanishad…

“And he who beholds all beings in the Self, and the Self in all beings, he never turns away from it. When to a man who understands, the Self has become all things, what sorrow, what trouble can there be to him who once beheld that unity?”

Verses 6 & 7

“All who worship what is not real knowledge (good works) enter into blind darkness; those who delight in real knowledge enter, as it were, into greater darkness. One thing, they say, is obtained from real knowledge; another, they say, from what is not knowledge. Thus we have heard from the wise who taught us this. He who knows at the same time both knowledge and not-knowledge overcomes death through not-knowledge, and obtains immortality through knowledge.”

Verses 9, 10, & 11