The mind is like wind, which cannot be grasped;

The mind is like water, which arises and ceases, non-abiding;

The mind is like flame, which is produced from myriad conditions;

The mind is like emptiness, in which defilements are impermanent.

── from Maharatnakuta Sutra
(Sutra of the Heap of Jewels)

The mind is like a monkey, for it is hard to tame; are you able to control your mind?

The mind is like a flash of lightning, in that it is as fast as a split second; are you able to grasp your mind’s intentions?

The mind is like a wild deer, in that it chases the sense objects; are you able to see through the illusions?

The mind is like a thief, such that it steals your merits; are you able to subdue the Mara in your mind?

The mind is like an adversary, for it causes suffering to the body; are you able to stop the maltreatment?

The mind is like a servant, for it is ordered about by afflictions; are you able to be remain amiable and carefree?

The mind is like a king, in that it has supreme power over the body; are you able to inspire virtue in people?

The mind is like an ever-flowing spring, in that it is inexhaustible; are you able to give to all sentient beings?

The mind is like an artist, as it paints everything; are you able to make the world a more beautiful place?

The mind is like space, in that it is boundless; are you able to embrace the entire world?

── from Renjian Fojiao Yulu
(Record of Teachings on Humanistic Buddhism)