Upanishad means receiving knowledge while sitting near the teacher. These are
conversations between self realized souls and their students on the subject matter of
Absolute truth. The philosophical aspects of all the important processes and practices of knowledge (known as vidyas) that are given in the Vedas are discussed in the Upanishads. Veda means knowledge and anta means end. Upanishads are known as Vedanta, end of knowledge.
The Upanishads philosophically establish the personal feature of the Absolute Truth as transcendental to material names, forms, qualities and actions. According to Muktika Upanisad, there are 108 Upanisads. Among these are:
Prayer beads chanted by Vaisnavas represent the 108 Upanisads which contain full knowledge of the Absolute Truth. Some Vaisnava transcendentalists also think that the 108 beads represent the 108 companions of Lord Krsna who participate in His rasa dance.
"When Lord Caitanya met Sarvabhauma Bhattacarya at Jagannatha Puri, Bhattacarya, being the greatest logician of the day, also wanted to teach the Lord Vedanta. Since Bhattacarya was an elderly man, the age of Lord Caitanya's father, He took compassion on the young sannyasi and requested Him to learn Vedanta-sutra from him. Otherwise, Bhattacarya maintained, it would be difficult for Lord Caitanya to continue as a sannyasi. When the Lord finally agreed, Bhattacarya began to teach Him in the temple of Jagannatha. Bhattacarya lectured on the Vedanta-sutra continuously for seven days, and the Lord heard him without speaking a word. On the eighth day, Bhattacarya said: "You have been hearing Vedanta-sutra from me for the past week, but You have not asked any questions, nor have You indicated that I am explaining it nicely. Therefore I cannot tell whether You are understanding me or not."
"I am a fool," the Lord replied. "I have no capacity to study Vedanta-sutra, but since you asked Me to hear you, I am trying to listen. I am simply listening to you because you said that it is the duty of every sannyasi to hear Vedanta-sutra. But as far as the meaning you are conveying is concerned--I cannot understand that." Thus the Lord indicated that in the Mayavadi sampradaya there are many so-called sannyasis who, even though illiterate and unintelligent, hear Vedanta-sutra from their spiritual master just as a matter of formality. Although they listen, they do not understand anything. As far as Lord Caitanya was concerned, He said that He did not understand the explanation of Bhattacarya not because it was too difficult for His understanding but because He did not approve of the Mayavadi interpretation.
When the Lord said that He was an uneducated fool and could not follow the expositions, Bhattacarya replied: "If You do not follow what I am saying, why don't You inquire? Why do You simply sit silently? It appears that You do have something to say about my explanations."
"My dear sir," the Lord replied. "As far as the Vedanta-sutra or the codes of Vedanta are concerned, I can understand the meaning quite well. However, I cannot understand your explanations. There is nothing really difficult about the meaning of the original Vedanta-sutra, but the way you explain Vedanta-sutra appears to obscure the real meaning. You do not elucidate the direct meaning but imagine something and consequently obscure the true meaning. I think that you have a particular doctrine which you are trying to expound through the codes of Vedanta-sutra."
....Lord Caitanya protested against misinterpretations of the Upanisads, and He rejected any explanation which did not give the direct meaning of the Upanisads. The direct interpretation is called abhidha-vrtti, whereas the indirect interpretation is called laksana-vrtti, The indirect interpretation serves no purpose. There are four kinds of understanding, called: (1) direct understanding (pratyaksa), (2) hypothetical understanding (anumana), (3) historical understanding (aitihya) and (4) understanding through sound (sabda). Of these four, understanding from the Vedic scriptures (which are the sound representations of the Absolute Truth) is the best method. The traditional Vedic students accept understanding through sound to be the best.
....According to Lord Caitanya, those who try to give personal interpretations to the Vedic statements are not at all intelligent. They mislead their followers by inventing their own interpretations. In India there is a class of men known as arya-samaja who say that they accept the original Vedas only and reject all other Vedic literatures. The motive of these people, however, is to give their own interpretation. According to Lord Caitanya, such interpretations are not to be accepted. They are simply not Vedic. Lord Caitanya said that the Vedic statements of the Upanisads are like sunlight. Everything is clear and very distinct when it is seen in the sunlight; the statements of the Vedas are similarly clear and distinct. The Mayavadi philosophers simply cover the sunlight with the cloud of misinterpretation.
Lord Caitanya then said that all the Vedic statements of the Upanisads aim at the ultimate truth known as Brahman. The word Brahman means "the greatest," and when we speak of the greatest we immediately refer to the Supreme Personality of Godhead, the source of all emanations. Unless the greatest possesses six opulences in full, he cannot be called the greatest. The greatest, who is full in six opulences, is the Supreme Personality of Godhead. In other words, the Supreme Brahman is the Supreme Personality of Godhead as well. In Bhagavad-gita (10.12) Krsna is accepted by Arjuna as the Supreme Brahman (param brahma). The conceptions of the impersonal Brahman and the localized Supersoul are contained within the understanding of the Supreme Personality of Godhead.
Whenever we speak of the Supreme Personality of Godhead, we add the word sri, indicating that He is full with six opulences. In other words, He is eternally a person; if He were not a person, the six opulences could not be present in fullness. If we say that the Supreme Absolute Truth is impersonal, we mean that His personality is not material. Thus in order to distinguish His transcendental body from ordinary material bodies, some philosophers have explained Him as being impersonal from the material point of view. In other words, material personality is denied, and spiritual personality is established. In the Svetasvatara Upanisad (3.19) it is clearly explained that the Absolute Truth has no material legs and hands, but in that scripture it is indicated that He has spiritual hands by which He accepts everything offered to Him. Similarly, He has no material eyes, but He does have spiritual eyes by which He can see everything and anything. Although He has no material ears, He can hear everything and anything. Having perfect senses, He knows past, future and present. Indeed, He knows everything, but no one can understand Him, for by material senses He cannot be understood. Being the origin of all emanations, He is the supreme, the greatest, the Personality of Godhead.
....According to a mantra in Taittiriya Upanisad (yato va imani bhutani jayante) this cosmic manifestation is but an emanation from the Supreme Absolute Truth, and it rests in the Supreme Absolute Truth. The Absolute Truth has been called the ablative, causative and locative performer. Thus as a performer, He is the Supreme Personality of Godhead, for these are symptoms of personality. As the ablative performer of this cosmic manifestation, all thinking, feeling and willing come from Him. Without thinking, feeling and willing, there is no possibility of arrangement and design in the cosmic manifestation. Then again, He is causative, for He is the original designer of the cosmos. And He is locative: that is, everything is resting in His energy. These attributes are all clearly attributes of personality.
In the Chandogya Upanisad (5.2.3), it is said that when the Supreme Personality of Godhead desires to become many, He turns over material nature. As also confirmed in Aitareya Upanisad (1.1), sa aiksata: "The Lord glanced at material nature." The cosmic manifestation did not exist before His glance; therefore His glance is not materially contaminated. His seeing power existed before the material creation; therefore His body is not material. His thinking, feeling and acting are all transcendental. In other words, it should be concluded that the mind by which the Lord thinks, feels and wills is transcendental, and the eyes by which He glances over material nature are also transcendental. Since His transcendental body and all His senses existed before the material creation, the Lord also has a transcendental mind and transcendental thinking, feeling and willing. This is the conclusion of all Vedic literature.
The word Brahman is found everywhere throughout the Upanisads. In Srimad-Bhagavatam, Brahman, Paramatma and Bhagavan, the Supreme Personality of Godhead, are all taken together as the Absolute Truth. Brahman and Paramatma realization are considered stages toward the ultimate realization, which is realization of the Supreme Personality of Godhead. This is the real conclusion of all Vedic literatures.
Thus according to the evidences afforded by various Vedic scriptures, the Supreme Lord Krsna is accepted as the ultimate goal of Brahman realization. Bhagavad-gita (Bg. 7.7) also confirms that there is nothing superior to Krsna. Madhvacarya, one of the greatest acaryas in Brahma's disciplic succession, has stated in his explanation to the Vedanta-sutra that everything can be seen through the authorities of the scriptures. He quoted a verse from Skanda Purana in which it is stated that the Rg Veda, Sama Veda, Atharva Veda, Mahabharata, Pancaratra and the original Ramayana are actually Vedic evidence. The Puranas, which are accepted by the Vaisnavas, are also considered to be Vedic evidence. Indeed, whatever is contained in that literature should be taken without argument as the ultimate conclusion, and all these literatures proclaim Krsna to be the Supreme Personality of Godhead."
Teachings of Lord Caitanya, Chapter 24
Bhaktivedanta Book Trust. HDG A.C. Bhaktivedanta Swami Srila Prabhupada.