Bhante on Buddha Nature
The Survey of Buddhism, pg 313

At the conclusion of Chapter Two we saw that, according to the distinctively Mahayana teaching, all beings are in possession of the Element of Buddhahood.  This Element is nothing but the reflection of the Absolute in the mirror of the so-called individual consciousness.  Only because they are in possession of this reflected image do beings feel an affinity for Enlightenment.  As the Ratnagotravibhaga says:

If the Element of the Buddha did not exist (in everyone),
There could be no disgust with suffering,
Nor could there be a wish for Nirvana
Nor striving for it, nor a resolve to win it. 

One of the strings of a musical instrument being struck, the corresponding string of the instrument beside it begins to vibrate.  When the devotee hears the music of Enlightenment, when they stand in the very presence of the Buddha, their own Element of Buddhahood starts vibrating.  Hence they know that the great being before them is striking upon the strings of their own heart the might chord of Supreme Enlightenment…

(‘he’ pronouns in last paragraph changed to ‘they’).