Who really is Chenrezig, deity with a white body and four, sometimes one thousand arms? Who is this deity for whom the Tibetans nourish a special devotion and whose meditation is now also practiced by many Westerners?….
First, we need to understand that Chenrezig is both an appearance, the divine manifestation as well as an essence, the inner reality, with one not excluding or contradicting the other. The appearance of Chenrezig is the symbol of his essence made manifest. Through this appearance we can approach the essence of Chenrezig. The appearance does not exhaust the essence anymore than the essence negates the appearance. To pretend that Chenrezig only has an existence outside ourselves would be a mistake. But it would also be a mistake to see him only as an abstraction. Grasping the link between the two aspects of the deity (appearance and essence) is necessary in order to understand both his nature and meditation….
Chenrezig is the mode of being of the mind that is the union of emptiness and compassion….He is the awakened nature of each being's own mind, the love and compassion primordially present in the dharmakaya [pure transcending awareness].
Chenrezig is within us because love and compassion are not qualities added to the mind. These qualities are part of the awakened state even if, for the moment, this state exists only as a potential for us….
Saying that Chenrezig is the ultimate nature of the mind does not negate his form manifestation. The essence expresses itself through an appearance. Chenrezig exists on the level of definitive meaning and also on the level of literal meaning where he appears in the form of the deity by which he is known. He is the visible expression taken by all the buddhas to help us activate the love and compassion that are presently only a potential in us and to reveal the ultimate Chenrezig to ourselves….
When we do the meditation of Chenrezig, if we see love and compassion grow in our mind, it is a sign that our practice is fruitful….
Every person whose heart is moved by love and compassion, who deeply and sincerely acts for the benefit of others without concern for fame, profit, social position, or recognition expresses the activity of Chenrezig. Love and compassion are the true signs revealing the presence of Chenrezig….
The mind of Chenrezig can work in the form of a human, an animal, a plant, or an inert thing. His mind is always the expression of compassion.

This explanation is excerpted with the kind permission of Clear Point Press, from the book entitled:
Chenrezig, Lord of Love by Bokar Rinpoche
published by Clear Point Press, P.O. Box 170658, San Francisco, CA 94117 ($9.95, softcover)
This book is an excellent source of information about the meditation of Chenrezig. It outlines the principles and methods of deity meditation and is an invaluable study guide. The author, Bokar Rinpoche, left Tibet for India at the age of 20 and competed two three-year retreats under the guidance of the great Tibetan master, Kalu Rinpoche. Because of his remarkable qualities and deep realization, he succeeded Kalu Rinpoche as head of the Shangpa Kagyu Lineage. He teaches advanced Vajrayana practices at monasteries in Northern India and Buddhist centers throughout the world.