In the early stages no student  can be expected to concentrate upon a nameless, formless and attributeless  Truth (Nirguna Brahman) which is at once omniscient, omnipotent and  omnipresent.  As an elementary training,  the mind needs some idea or ideas or pedestal to fix its attention on and after  wading through those ideas to come to the central theme of the Upanishad. Thus  in all Upasanas the modus operandi is to tie down the mind with a central idea  and allowing it to roam about within that limited mainstay just like allowing  the freedom to a cow on the grazing ground when fixed to a peg with a long  rope.
For example, after installing a  stone, the devotee superimposes the siva-tattva upon it and meditates on Mahesvara through that planted stone. Here the devotee  recognizes Mahesvara in the stone and not a stone in Mahesvara. So too, the  Vedic Rishi  had to supply a substratum, tangible and known to the students, before he could make them superimpose upon that symbol the ideas of larger and  vaster Truth enunciated in the Upanishad. Once this technique is understood,  all the Upasanas mentioned in this section become sufficiently clear and  self-evident. Now the question is what is that tangible and known substratum or  symbol?
As the students are proficient  in Sanskrit language, they are familiar with the conjunction of syllables and  joining of words or combination which is called Sandhi or Samhita as also  their disjoining. If two components are joined they become a compound.  There are four parts or elements or limbs in  such compound words as under:
  
Purva rupam - the earlier form (prior)
  
Uttara rupam - the latter form (posterior)
  
Sandhih - the combination between the above two forms, and
  
Sandhanam - that by which such connection is brought about.
An example will make this clear.  In the compound word ‘Mahesvara’ the  two limbs are an adjective and a noun viz. Maha and Isvara. The first word ‘Maha’ is  called Purva Rupam or earlier form. The word ‘Isvara’ that follows is Uttara  Rupam or the latter form. The sound ‘A’ in the Purva Rupam and the sound ‘I’ in the Uttara Rupam when joined becomes the sound ‘E’ in the compound which is called Sandhi or Samhita and the act  of joining is Sandhanam.
Thus the term ‘Samhita’ means  conjunction or union, especially the combination of letters according to  pleasantness of sounds. The philosophical observations presented in this  section are based on this linguistic phenomenon
Samhita in grammar is closely  related to the science of phonetics which we have seen in the earlier section.  As the students had a very clear idea about the construction of a compound  word, the teacher had chosen ‘compound word and its structure’ as substratum  for his students to superimpose certain prescribed ideas so that they could  meditate upon them. With the help of the principle underlying the combination of  words and letters, some greater relations that exist between objects of  universal importance are mentioned to assist the student in subtle thinking on  a large scale.
The superimposition upon the  combination of words as advised here fall under five headings. They represent  the five different fields of independent thinking superimposed upon the limbs  of the compound words. They are:
  
Adi lokam - knowledge concerning the universe
  
Adi jyotisham - knowledge concerning light - luminosity
  
Adi Vidyam - knowledge concerning vidya or flow of Upanishad knowledge
  
Adi Prajam - knowledge concerning progeny (maintaining family line) and
  
Adi Atmam - knowledge concerning oneself as a human being
These five objects of thought  chosen for meditation are called ‘Maha Samhita’ – Great Combinations leading to  and sustaining one's mind in God-consciousness. They are considered great  because, as objects of thought, they are of infinite scope, and hence easily  recognized as the very glories of the Supreme. This kind of contemplating on  the unknown through the known is more or less like Bhagavan Sri Krishna’s  description of the Supreme as His various Vibhutis in the 10th  Chapter of the Bhagvad Gita.
Now, the Upanishad tells how this Upasana is practiced in terms of the four elements referred to above.
MANTRA 1 
saha nau yashah . saha nau brahmavarchasam.h athatah sa.nhitaya upanishadam vyakhyasyamah..pa~nchasvadhikaraneshu..adhilokam..adhijyautisham..adhividyam.. adhiprajamadhyatmam.h . ta mahasa{\m+} hita   ityachaxate..1
May glory come on both of us together! May the light of Brahman shine alike through both of us! Now we will explain the Upanishad on the Samhita (combinations) under five heads: with regards to the worlds, the heavenly lights, knowledge, progeny and the atman (body). People call these the great Samhitas. 
This is a prayer for glory arising out of noble living and high thoughts. It begs of the light of Brahma Varchasam i.e. sanctity and pre-eminence which one achieves by a life devoted to sacred knowledge and realization of the Supreme Reality through Tapas.
The teacher tells the students that now we shall expound the doctrine of combination of words based on the five perceptible objects – universe, light, learning, progeny and self. The observations of these five objects are together called ‘the great combinations’. 
MANTRA 2-6 
athadhilokam.h .prithivi purvarupam.h . dyauruttararupam.h .
akashah sandhih . vayuh sandhanam.h . ityadhilokam.h . . 2...
First, with regard to the worlds: The earth is the first form, heaven is the last from, the akasa is the union and the air is the medium. Thus with regard to the worlds. 
athadhijautisham.h . agnih purvarupam.h . aditya uttararupam.h . apah sandhih .
vaidyutah sandhanam.h . ityadhijyautisham.h . . 3
Next, with regard to the heavenly lights: Fire is the first form, the sun is the second form, water is the union and lightning is the medium. Thus with regard to the heavenly lights. 
athadhividyam.h .acharyah purvarupam.h…antevasyuttararupam.h . vidya sandhih . pravachana{\m+}  sandhanam.h . ityadhividyam.h …4
Next, with regard to knowledge: The teacher is the first form, the pupil is the second form, knowledge is the union and the recitation is the medium. Thus with regard to knowledge. 
athadhiprajam.h . mata purvarupam.h .pitottararupam.h . praja sandhih . prajanana{\m+}  sandhanam.h .ityadhiprajam.h ...5
Next, with regard to progeny: The mother is the first form, the father is the second form, the progeny is the union and procreation is the medium. Thus with regard to the progeny. 
athadhyatmam.h . adhara hanuh purvarupam.h . uttara hanuruttararupam.h . vaksandhih . jihva sandhanam.h . ityadhyatmam.h …6
Next, with regard to atman: The lower jaw is the first form, the upper jaw is the second form, the speech is the union and the tongue is the medium. Thus with regard to the atman. 
The above five Mantras (2-6) explain how to meditate on the five perceptible objects viz. universe, light, learning, progeny and self superimposing on them the idea of the four elements that go into the combination of words. One should meditate on these five objects keeping in mind the interior-relationship between the four elements embedded in them. This is put in plain words by means of a table given below.
  
    
      Objects  for meditation  | 
      Purva rupam 
    (Prior form)   | 
      Uttara rupam 
    (Latter form)   | 
      Sandhih 
    (Union)   | 
      Sandhanam 
    (Means of joining)   | 
    
    
      Universe  | 
      Earth  | 
      Heaven  | 
      Akasa  | 
      Air  | 
    
    
      Light  | 
      Fire  | 
      Sun  | 
      Water  | 
      Lightning  | 
    
    
      Knowledge   | 
      Teacher  | 
      Pupil  | 
      Knowledge   | 
      Recitation  | 
    
    
      Progeny  | 
      Mother   | 
      Father  | 
      Progeny  | 
      Procreation  | 
    
    
      Self Atman  | 
      Lower jaw  | 
      Upper jaw  | 
      Speech  | 
      Tongue  | 
    
  
The whole process of meditation described above helps to contemplate the Vastness of Cosmos as an inter-related whole including all existence in a grand totality (purnamadah purnamidam). By doing so the mind attunes itself to the infinite, going beyond trifling mundane pre-occupations.
MANTRA 7
itima mahasa{\m+} hitah . ya evameta mahasa{\m+} hita vyakhyata veda . sandhiyate prajaya pashubhih . brahmavarchasenannadyena suvargyena lokena …7
               iti tritiyo.anuvakah ..
These are the great Samhitas (combinations). He who meditates on these Samhitas, as here explained, becomes united with progeny, cattle, the light of Brahman, food and the heavenly world.  
As these Mantras are addressed to the students who have to go back to the society and lead a householder’s life, the material rewards that may accrue to them by going through such Upasana are enumerated here.  It is expected that they will slowly grow in stature in their inner constitution of mind and intellect.
End of Section 3 - Chapter 1
We shall take up Section 4 of  Chapter 1 next time.
HARIH OM