Shankaracharya, Gumbirangi Maharaj says samadhi is not the highest. It helps you to attain the highest, which is realization that you are Brahman. The teaching on meditation is given here. What we are trying to do in meditation, that's pointed out. That's taught here.
Swami Sarvapriyananda teaches the Katha Upanishad, one of India's most revered texts which is also a part of the Vedas. It is a collection of philosophical poems representing a conversation between the sage Naciketas and Yama (god of death). They discuss the nature of Atman, Brahman and Moksha(liberation).