A really cool metaphor used to describe yoga is as follows (from the ancient text the Bhagavad Gita, summarized here by Max Strom): 

“There’s a wonderful metaphor from the yoga tradition that vividly depicts the plight of the average person and points the way to a more meaningful life. It’s the carriage allegory. 

• Carriage = body

• Horses = emotions

• Driver = mind

• Passenger = soul. 

The story goes that the state of the average person is as follows; the carriage is in terrible disrepair, the horses are half-wild, the driver is unfocused and drunk, and the passenger is asleep. The passenger, a king or queen, is asleep, dreaming he/she is a prisoner. Yoga, it is said, repairs the carriage (body), tames the horses (emotions), sobers and focuses the driver (mind), and ultimately - reawakens the passenger (soul). The soul then remembers their true purpose and instructs the driver on which route to take to their ultimate destination. This is the purpose of yoga, anything less is simply exercise.”

What is YOGA Pt. 1