Listen!
(Source: Taitreya Upanishad)

Meaning:
Let us all grow together, enjoy together, perform heroic deeds together; let our strength of intellect come together, let the bright intellects shine, and let us live without any hatred.

In a nutshell Sahana is togetherness, and hence conveys the message “Unity is Divinity”

UPDATE: Here is another viewpoint of the above shanti mantra. This is in the light of student and the teacher (Guru).

Meaning:
Let both of us protect each other together (teacher and pupil), may both of us enjoy together (the knowledge & liberation), may both of us work together, let our study become radiant, let there be no hatred between us, OM Peace, Peace, Peace.

As the verse suggests, there should be a perfect harmony between the student and his teacher. To carry out a substantial research (spiritual or material), there is a great deal of mentoring required behind the scenes… and eventually results in the making of a great student.

I am reminded of how Swami Vivekananda brought glory to his master Sri Ramakrishna Paramahamsa. A perfect disciple for a perfect guru.

Ref: Wikipedia