One-pointed devotion, full determination, and dedication lead him to the higher step called nididhyāsana. Here he acquires comprehensive knowledge of the Ultimate Truth. But he has not yet attained the final step of consciousness that leads him to the direct realization of the one self-existent Truth without second. The highest state of contemplation is called sāksātkāra. In this state, perception and conceptualization are in complete agreement, and all the doubts from all levels of understanding vanish forever. At this height of knowledge, truth reveals itself to the aspirant, and perfect realization is accomplished, “I am Ātman—I am Brahman.” This state of advaita is attained by the process of contemplation.
First, an aspirant attentively listens to the sayings of the Upanishads from a preceptor who is Brahman-conscious all the time. In the second step, he practices vichāra (contemplation), which means that he goes to the depths of the great sayings and determines to practice them with mind, action, and speech.
~ Swami Rama, from “Enlightenment without God” commentary of Mandukya Upanishad