In the Bhagavad-gītā, oṁkāra or praṇava, is glorified as a direct representation of the Supreme Personality of Godhead. Therefore if at the time of death one simply remembers oṁkāra, he remembers the Supreme Personality of Godhead and is therefore immediately transferred to the spiritual world. Oṁkāra is the basic principle of all Vedic mantras, for it is a representation of Lord Kṛṣṇa, understanding of whom is the ultimate goal of the Vedas, as stated in the Bhagavad-gītā (vedaiś ca sarvair aham eva vedyaḥ). Māyāvādī philosophers cannot understand these simple facts explained in the Bhagavad-gītā, and yet they are very proud of being Vedāntīs. Sometimes, therefore, we refer to the Vedāntī philosophers as Vidantīs, those who have no teeth (vi means “without,” and dantī means “possessing teeth”). The statements of the Impersonalist philosophy, which are the teeth of the Māyāvādī philosopher, are always broken by the strong arguments of Vaiṣṇava philosophers such as the great ācāryas, especially Rāmānujācārya. Śrīpāda Rāmānujācārya and Madhvācārya break the teeth of the Māyāvādī philosophers, who can therefore be called Vidantīs, “toothless.”
Ref >> Srila Prabhupada Vani.