At the early age of 14, Sri Sathya Sai Baba revealed His future mission in a letter written to His elder brother, Seshama Raju:

Dated: 25 May 1947

To all who are devoted to me:
My Dear One! I received the communication that you wrote and sent; I found in it the surging floods of your devotion and affection, with the undercurrents of doubts and anxiety. Let me tell you that it is impossible to plumb the hearts and discover the natures of Jnanis (those who have acquired spiritual wisdom), yogis, ascetics, saints, sages, and the like. People are endowed with a variety of characteristics and mental attitudes; so each one judges according to his own angle, talks and argues in the lights of his own nature.
But we have to stick to our own right path, our own wisdom, our own resolution, without getting affected by popular appraisal. As the proverb says, it is only the fruit-laden tree that receives the showers of stones from passers-by. The good always provoke the bad into calumny; the bad always provoke the good into derision. This is the nature of this world. One must be surprised if such things do not happen.
The people too have to be pitied, rather than condemned. They do not know. They have no patience to judge a right. They are too full of lust, anger and conceit to see clearly and know fully. So, they write all manner of things. If they only knew, they would not talk or write like that. We, too, should not attached any value to such comments and take them to heart, as you seem to do. Truth will certainly triumph some day; untruth can never win. Untruth might appear to overpower truth, but its victory will fade away and truth will establish itself.
It is not the way of the great to swell when people offer worship and shrink when people scoff. As a matter of fact, no sacred text lays down rules to regulate the lives of the great, prescribing the habits and attitudes that they must adopt. They themselves know the path they must thread; their wisdom regulates and makes their acts holy. Self-reliance, beneficial activity—these two are their special marks. They may also be engaged in the promotion of the welfare of devotees and in allotting them the fruits of their actions. Why should you be affected by tangle and worry, as long as I am adhering to these two? After all, the praise and blame of the populace do not touch the Atma, the reality; they can touch only the outer physical frame.
I have a task: to foster all mankind and ensure for all of them lives full of Ananda (bliss). I have a vow: to lead all who stray away from the straight path back again into goodness and save them. I am attached to a "work" that I love: to remove the sufferings of the poor and grant them what they lack. I have a 'reason to be proud' for I rescue all who worship and adore me, aright. I have my definition of the 'devotion' I expect: those devoted to me to have to treat joy and grief, gain and loss, with equal fortitude.


This means that I will never give up those who attach themselves to me. When I am thus engaged in my beneficial tasks, how can my name ever be tarnished, as you apprehend? I would advise you not to heed such absurd talk. Mahatmas (great souls) do not acquire greatness through some one calling them so; they do not become small when someone call them small. Only those low ones who revel in opium and ganja but claim to be unexcelled yogis, only those who quote scriptural texts to justify their gourmandry and pride, only those who are dry-as-dust scholars exulting in their casuistry and argumentative skills, will be moved by praise or blame.
You must have read life-stories of saints and divine personages; in those books you must have read even worse falsehood and more heinous imputations cast against them. This is the lot of mahatmas everywhere, at all times. Why then do you take these things so much to heart? Have you not heard of dogs that howl at the stars? How long can they go on? Authenticity will soon win.
I will not give up my mission, nor my determination. I know I will carry them out; I treat the honor and dishonor, the fame and blame that may be the consequence, with equal equanimity. Internally, I am unconcerned. I act but in the outer world; I talk and move about for the sake of the outer world and for announcing my coming to the people, else I have no concern even with these.
I do not belong to any place, I am not attached to any name. I have no "mine" or "thine." I answer, whatever the name you use. I go, wherever I am taken. This is my very first vow. I have not disclosed this to anyone so far. For me the world is something afar, apart. I act and move only for the sake of mankind. No one can comprehend my glory, whoever he is, whatever his method of inquiry, however long his attempt.
You can yourself see the full glory in the coming years. Devotees must have patience and forbearance.
I am not concerned nor am I anxious that these facts should be made known; I have no need to write these words, I wrote them because I felt you will be pained if I do not reply.
Thus,

your Baba