Adi Sankaracharya :
Chaos pervaded all through India in the matter of religion and philosophy. Sect after sect, such as Charvakas, Lokayathikas, Kapalikas, Shaktas, Sankhyas, Buddhas and Madhyamikas sprang up. The number of religions rose as high as seventy-two. There was fight amongst sects. There was no peace anywhere. Chaos and confusion reigned supreme. There was superstition and bigotry. Darkness prevailed over the once happy land of Rishis, sages and Yogins. The once glorious land of the Aryans was in a miserable state. Such was the state of the country at the time which just preceded the Avatara (incarnation) of Sankaracharya.
The existence of Vedic Dharma in India today is due to Sankara. The forces opposed to Vedic religion were more numerous and powerful at the time of Sankara than they are today. Still, single-handed, within a very short time, Sankara overpowered them all and restored the Vedic Dharrna and Advaita Vedanta to its pristine purity in the land. The weapon he used was pure knowledge and spirituality. The previous Avataras, like Rama and Krishna, used physical forces because the obstacles to Dharma in those days arose from the physical obstructions and molestations of the Asuras (demons). The menace to Dharma in the Kali age (age of destruction) arose from obstacles that were more internal than external, more mental than physical. The seeds of Adharma (unrighteousness) were then working in the minds of almost everyone. Hence the evil had to be combated purely by the weapon of knowledge and self-purification. It was in order to forge this weapon and wield it with efficacy that Sankara took birth in the Brahmin Varna (caste) and entered the Sannyasa (renunciate) order early in life. The previous Avataras like Rama and Krishna took birth in the Kshatriya Varna (warrior caste), because in their days they had to wield military weapons in the restoration of Dharma.
All are no doubt aware of the very important position assigned to Sankaracharya in the history of Indian philosophy. It can be affirmed, without any fear of contradiction, that Bharata Varsha would have ceased to be Bharata Varsha several centuries ago and would never have survived the murderous sword, the devastating fire and the religious intolerance of the successive invaders, if Sankara had not lived the life he lived and taught the lessons he taught. And those lessons are still pulsating in every cell and in every protoplasm of the true aspirant and the true Hindu.