Om sahanāvavatu sahanaubhunaktu sahavīryaṃ karavāvahai
Tejasvināvadhitamastu mā vidviśāvahai
Om śāntiḥ śāntiḥ śāntiḥ

This mantra, found in the Taittiriya Upanishad, is most propitious for recitation before study with the teacher.

Here is one translation:
May He protect us both together. May he nourish us both together. May we both acquire strength together. Let our study be brilliant. May we not cavil at each other. Om! Peace! Peace! Peace!
(Translated by Swami Gambhirananda).

Unfolded by a traditional teacher, these simple statements reveal their inner meaning.

Swamini Atmaprakasanda’s exposition of the first line:
Saha : together
Nau : us two
Avatu : may (the Lord) protect

 Bhunaktu : may (the Lord) nourish
vīryaṃ : strength
karavāvahai : may we two have

The word saha (together) is key because it applies to both teacher and student. The accusative form of ‘us two’, nau, becomes nāv and then nā due to sandhi rules for the euphonic combination of sounds. This prayer is from the student and requests three things.

1. That the Lord protects student and teacher. This mantra is a request for protection, avatu (third person imperative form av: ‘to guard, defend , protect , govern’) – may (the Lord) protect. Protection is twofold – absolute and relative. Absolute protection comes from jñānam, knowledge. Fear, which is based on the perception of two, disappears, and maturity grows through knowledge. Vairāgyam (dispassion) is born from knowing the limitations of everything. Relative protections are such things such as good health, shelter, food, etc.

2. That the Lord nourishes student and teacher. Nourishment, bhuj, here is the means of relative protection. It stands for all that is required to help us in life: food, shelter, etc ­– all that contributes to a proper conducive atmosphere in which we can grow and knowledge can thrive. Bhunaktu – (third person imperative form bhuj) – may (the Lord) nourish.

3. That student and teacher have the necessary strength. Vīryaṃ, strength, is also a means of protection. It stands here for the physical and emotional strength to tackle prārabdha. Karavāvahai (1st Per./dual/imperative) ‘may we two have’.

 May knowledge protect us both – teacher and student together – by giving us the vision of unity in which there is an absence of fear, and the growth of maturity and discrimination. Together may we be nourished by being provided with conducive circumstances that support the establishment of knowledge. And, together, may we have the physical and emotional strength to face prārabdha with equanimity.

—
Tejasvinā: by inner glow
Avadhitam astu: may be well understood (by me)
Mā: never
Vidviśāvahai: may there be hatred.

Swaminiji’s exposition of the second line:

It’s said that the above three statements deal with the prayer for the protection of both teacher and student together. The statements that follow refer to just the student alone.

Tejasvinā is the singular, instrumental form of masculine noun tejasvin – the glow that comes from inner composure and tranquillity. The verb to be supplied is bhaviyam [May I be]. This statement thereby means: ‘may I be tejasvi – one that is lit by that inner glow’.

Adhitam means ‘learned well’. Avadhitam means ‘understood well’. Avadhitam astu – ‘may (the Upanishad) be well understood (by me)’.

Mā vidviśāvahai. literally translates as may we not hate one another. But why is there talk of hatred? Here it means ‘may there not be a communication gap between us’.

These are also forms for protection (avana).

—
Om śāntiḥ śāntiḥ śāntiḥ

Swaminiji’s exposition:
The three repetitions of śāntiḥ is to pray for peace from the three ‘heats’ (tāpaḥ): adhyātmika – arising from my own being; adhibhautika – arising from conditions outside myself (over which I may be able to exert some control); adhidavika – arising from nature (over which I have no control).

May I be lit by the glow that comes from inner composure. May the Upanishadic vision be well understood by me. May there be no communication gap between me and my teacher.

May there be peace from inner afflictions, may there be peace from outer afflictions, may there be peace from god-made afflictions.

Final translation:

May he protect us both together (through the vision of advaita).
May he nourish us both together (by giving us the circumstances in which the vision can flourish).
May we have strength together (to face what’s presented with poise).

May I have that glow (of inner composure).
May I understand well (the Upanishadic vision).
May there be no communication gap (between me and my teacher).

May peace and peace and peace be everywhere.