The upanayana of a boy is performed when he is old enough to understand things and chant the mantras. During this ceremony he is asked to go begging for alms. "Bhiksacaryam cara", he is told. "Badham", he replies( "I will do so"). So, before his upanayana, the child must know enough Sanskrit to understand what is meant by "Bhicksacaryam cara". When he starts learning at the age of five he will have a basic knowledge of Sanskrit by the time he is eight years old, the age fixed for the upanayana samskara.
The world will stand to gain if eight-year-old children wear the sacred thread, have sufficient knowledge of Sanskrit and chant the Gayatri mantra. Today things have so changed that Godlessness is thrust into tender minds.
Upa=near; nayana=to take or lead(a child). Near whom or what is (the child) taken? Near the guru. That is what upanayana means. Who is a guru? One who has mastered the Vedas. There is one guru during the brahmacaryasrama (student-bachelorhood) and another during the last asrama of sannyasa. The first guru is learned in the Vedas, Vedangas and so on while the second is one who has forsaken all including the Vedas. In the first asrama you acquire vidya; in the last asrama you realise jnana. .
Upanayana is initiation into the brahmacaryasrama while "samavartana" is the completion of this stage of life. "Samavartana" means "return". To repeat, from the upanayana to the samavartana is student-bachelorhood or the brahmacaryasrama. Samavartana thus denotes returning home on completing one's study of the Vedic discipline in the gurukula.
Upanayana is the "purvanga" of student-bachelorhood. Any "anga" must have something that gives its distinctive character. This is called "angi". Thus for the anga called upanayana the angi is brahmacarya. The word "Brahma" has six different meanings. In the tern "Brahmacarya" it means the Vedas. An entire asrama or stage in life is set apart for the study of the Vedas: this is brahmacarya. The minimum period for student-bachelorhood is twelve years which is the time taken to master the Vedas.
"Brahma" also means Visnu as well as Siva. The word, in addition, is also used to denote a Brahmin, tapas or austerities and the Paramatman. When you say Brahma with a long "a" at the end (Brahma) it means the Creator.
At mealtime we do "parisecana", that is we sprinkle water over our food, say, rice. It is the anga for the meal. The rice must be eaten o1nly after it has ceremonially been made a prasada of Isvara. This is the purpose of the parisecana. Is it not foolish to refuse the food after it has been made a prasada of Isvara. Not to learn the Vedas after one has had the upanayana is akin to refusing to eat the food placed before one after one has done the paricesana. In this sense the majority of people who have had their upanayana must be called foolish.
There are four "vratas" between the purvanga called the upanayana and the uttaranga called the samavartana. These are prajapatya, saumya, agneya, and vaisvadeva [see following para].
There are certain rules to be followed to master a mantra. The Vedas are replete with mantras that help you to go forward spiritually and find release from worldly existence. "Brahmacarya" may be described as the total discipline required to master the Vedas. There are also rules meant for the study of each part of these scriptures. Each Veda has four "kandas", each associated with a great sage. Brahmayajna is performed in honour of them. For each kanda there is also a separate vrata. During student-bachelorhood when a kanda is studied its vrata must also be observed. The kandas are prajapatya, saumya, agneya and vaisvadeva. After completing the four kandas the pupil will have his samavartana with the permission of his guru.
The four vratas mentioned above are for students of the Krsna-Yajurveda. For students of the Rgveda there are the Mahanamni, Maha, Upanisad and Godana vratas. Thus each Veda has its own vratas. I mentioned those for the Krsna-yajurveda first since it is widely followed [in the South].
Samavartana is also called "snana" and one who has gone through it is a "snataka". Everybody must learn his own Veda [the Veda that is his by birth] and other subjects in addition. When we perform upakarma we must start learning a new part of the Vedas. Later, at the time of utsarjana, it must be discontinued and the study of the Vedangas taken up. The Vedas, to repeat, must be studied during the six months roughly of Daksinayana, from the south of Sravana to Taisya. The next six months must be devoted to the Vedangas.
To master the mantras the student must strictly observe the rules pertaining to the brahmacaraya and to the particular part of the Veda that is being studied. Nowadays we do not observe anything, we do not even learn the Vedas or a part thereof. Before the wedding ceremony, we perform a rite called "vrata": in one hour we go through a number of samskaras without understanding what we are doing and why we are doing them. Perhaps, I find myself giving this discourse because so much at least survives of the Vedic tradition.
The importance of the upanayana ceremony lies in this: it makes a person fit to receive instruction in the Vedas and spread their divine power throughout the world. Parents must realise this fact and perform their son's upanayana at the right time.
"Dvi-ja" ("iru-pirappalan" in Tamil) is the name given to a Brahmin, Ksatriya or Vaisya. They merit the second birth only when they become qualified to learn the Vedas. Such a birth is meant, as mentioned earlier, to spread the divine power all over the world, and it is through the upanayana ceremony that they become qualified for it. Performing this ceremony at the right time is the responsibility of the parents. At present, in matters like this, no regard is paid to the canons. In contrast, in the old days, people had faith in the scriptures and acted according to their dictates.
For a general background, please see here