by Shiva Bear – A commentary on the Jewel Ornament of Liberation by Gampopa (1074-1153 C.E.)

Without cause, no effect – on what basis can Buddhahood exist?

This question is traditionally answered using the metaphor of the seed: Even if a seed (the cause) is planted in the ground it will not grow without the right conditions like water, nutrients in the soil and sunlight and so on. Hence if all beings were permeated by Buddha nature it would not develop without the right conditions. However without a seed no matter the conditions no plant (the effect) can grow.

The Sutra of the Great Parinirvana says:
For example, as butter permeates milk, likewise the Essence of
the Thus-gone One pervades all sentient beings.

The oil in the seed is no different from the oil that can be pressed from the seed but until it is actually pressed out of the seed it cannot be called oil. First the necessary conditions (causes) must be applied in the production. In the same way all living beings contains Buddha nature (bodhicitta) but is not fulfilling the complete potential until the full development of mind.

The Ten Noble Bhumis Sutra says
The family of wise bodhisattvas
Can be recognized by its signs
Just as fire is known by its smoke
And water is known by water birds

The point is that all beings hold the seed for Buddha nature and have the possibility to develop it, thereby reaching enlightenment.