When all the knots of the heart are untied, then and there the mortal man becomes immortal. This is the whole teaching.
Katha Up. – 6.15
When, my dear, Atman is seen, heared about, reflected upon and contemplated on, all this universe becomes known. (Yajnavalkya teaching his wife Maitreyi)
Brihadaryanika Up. – 4.5.6