Compassion is the cause of Bodhi Mind, while the root of compassion is loving kindness.
Through the practice of loving kindness, the Bodhi Mind is aroused with clear determination for buddhahood and aspiration to be a bodhisattva to help all sentient beings.
To develop loving kindness, imagine your mother right before you while the following thought is brought to mind,
"My kind mother produced this body I have, an effort which caused her a lot of hardship and trouble. She gave me this precious life, taken care of me, and performed every single action needed for my survival in this world.
"Regarding me with a love greater than she had for her self, she protected me, and gave me all the help and support that I needed to grow up. When threatened by harm, she protected me, which is a great kindness. It would be truly amazing if my mother was happy and at ease, but it is not just my present mother — in all my countless lives, I have had mothers who have done exactly the same, loving mothers who have bestowed on me the same kind of help and love.
"This happened not only once, as a mother, but also countless times as a friend, a lover, and a companion. All these people have helped me in all kinds of ways. Thinking of my mother who is very dear to me and helped me, I now want to return her kindness."
Aroused in our hearts by such a thought, loving kindness should become a distinct and truly real feeling.
- Tulku Urgyen Rinpoche & Tulku Adeu Rinpoche, Skillful Grace: Tara Practice for Our Time