"The Mayavadi philosophy is veiled Buddhism." In other words, the voidist philosophy of Buddha is more or less repeated in the Mayavadi philosophy of impersonalism, although the Mayavadi philosophy claims to be directed by the Vedic conclusions. Lord Siva, however, admits that this philosophy is manufactured by him in the age of Kali in order to mislead the atheists."
Teachings of Lord Caitanya, Chapter 19
"....Sankaracarya taught that the Absolute Truth is impersonal, and thus he indirectly denied the existence of God. Sankaracarya's mission was special; he appeared to reestablish the Vedic influence after the influence of Buddhism. Because Buddhism was patronized by Emperor Asoka, twenty-six hundred years ago the Buddhist religion practically pervaded all of India. According to the Vedic literature, Buddha was an incarnation of Krsna who had a special power and who appeared for a special purpose. His system of thought, or faith, was accepted widely, but Buddha rejected the authority of the Vedas. While Buddhism was spreading, the Vedic culture was stopped both in India and in other places. Therefore, since Sankaracarya's only aim was to drive away Buddha's system of philosophy, he introduced a system called Mayavada.
Strictly speaking, Mayavada philosophy is atheism, for it is a process in which one imagines that there is God. This Mayavada system of philosophy has been existing since time immemorial. The present Indian system of religion or culture is based on the Mayavada philosophy of Sankaracarya, which is a compromise with Buddhist philosophy. According to Mayavada philosophy there actually is no God, or if God exists, He is impersonal and all-pervading and can therefore be imagined in any form. This conclusion is not in accord with the Vedic literature. That literature names many demigods, who are worshiped for different purposes, but in every case the Supreme Lord, the Personality of Godhead, Visnu, is accepted as the supreme controller. That is real Vedic culture.
The philosophy of Krsna consciousness does not deny the existence of God and the demigods, but Mayavada philosophy denies both; it maintains that neither the demigods nor God exists. For the Mayavadis, ultimately all is zero. They say that one may imagine any authority--whether Visnu, Durga, Lord Siva, or the sun-god--because these are the demigods generally worshiped in society. But the Mayavada philosophy does not in fact accept the existence of any of them. The Mayavadis say that because one cannot concentrate one's mind on the impersonal Brahman, one may imagine any of these forms. This is a new system, called pancopasana. It was introduced by Sankaracarya, but the Bhagavad-gita does not teach any such doctrines, and therefore they are not authoritative.
The Bhagavad-gita accepts the existence of the demigods. The demigods are described in the Vedas, and one cannot deny their existence, but they are not to be understood or worshiped according to the way of Sankaracarya.
Science of Self-Realization, Chapter 3
"Sankaracarya's philosophy is to get out of this combination of material elements and become situated in our original, spiritual position. Thus the Mayavadis' motto is brahma satyam jagan mithya: "Brahman, the Absolute, is true, and this material creation is false." Sankaracarya rejected Buddha's philosophy, which gives no information concerning the spirit soul. Buddha's philosophy deals only with matter and the dissolution of matter; thus the goal of Buddhism is to merge into the voidness.
Both Buddhism and Mayavada philosophy reveal only partial truth. Sankaracarya's Mayavada philosophy accepts Brahman, spirit, but does not describe spirit in its fullness. Mayavada philosophy teaches that as soon as we become cognizant of our existence as Brahman (aham brahmasmi), then all our activities come to a stop. But this is not a fact. The living entity is always active. It may seem that in meditation one can stop all sensual activity, but still one is meditating, and that is also action.
While meditating on Brahman, the Mayavadi thinks, "I have become God." In one sense, of course, it is correct to think, "I am one with God," for as spirit souls we are all one with God in quality. But no one can ever become quantitatively one with God. In the Bhagavad-gita (15.7) Krsna declares that the living entities are "part and parcel of Me." Krsna is completely spiritual (sac-cid-ananda), so each particle of spirit must also be sac-cid-ananda, just as a gold earring is qualitatively one with the gold in a gold mine. Still, the gold earring is not the gold mine.
So the Mayavadis' mistake is to think that the part can become equal to the whole. They presume that because they are part and parcel of God, they are God. Therefore the Srimad-Bhagavatam (10.2.32) describes the impersonalists as avisuddha-buddhayah: "Their intelligence is impure; they are still in ignorance." Mayavadis believe that by accumulating knowledge they become one with God, and thus they address one another as "Narayana." That is their great mistake. We cannot become Lord Narayana. Narayana is vibhu, which means "very big" or "infinite," whereas we are anu, infinitesimal. Our spiritual magnitude measures one ten-thousandth of the tip of a hair. Therefore how can any sane man claim that he has become God?
Sankaracarya gave a hint about Brahman, teaching everyone to think, aham brahmasmi, "I am the spirit self, not the material body." The Vedas agree. One who is situated in mukti, or liberation, understands perfectly, "I am not this body; I am pure spirit soul." But that is not the end of self-realization. Next one has to ask, "If I am an eternal spirit soul, what is my eternal spiritual activity?" That eternal activity is devotional service to Krsna.
In the Bhagavad-gita (18.54) Lord Krsna describes how Brahman realization leads to devotional service:
na socati na kanksati
samah sarvesu bhutesu
mad-bhaktim labhate param
"One who is transcendentally situated at once realizes the Supreme Brahman and becomes fully joyful. He never laments or desires to have anything. He is equally disposed toward every living entity. In that state he attains pure devotional service unto Me."
Often big svamis talk about attaining "Brahman realization" but do not remove themselves from worldly pleasures and pains. They involve themselves in humanitarian activities, thinking, "My fellow countrymen are suffering; let me open a hospital" or "They are uneducated; let me open a school." If someone is really on the platform of brahma-bhutah, why would he accept any particular place as his country? Actually, as spirit souls we do not belong to any country. We get a body, and as soon as the body is finished, the connection with a particular country is also finished. The symptom of lamentation reveals that the so-called liberated person has not been cured of his attachment to worldly pleasure and pain. That means he has not become joyful, because one who is joyful does not lament. So many learned sannyasis have fallen down to material activities because they have not in fact realized Brahman. It is not so easy. As already explained, the influence of the modes of nature is very strong. The living entity entangled in different types of fruitive activity is like a silkworm trapped in a cocoon. Getting free is very difficult unless one is helped by the Supreme Personality of Godhead."
A Second Chance, Chapter 11
Bhaktivedanta Book Trust. HDG A.C. Bhaktivedanta Swami Srila Prabhupada.