What is real?

"What is 'real'? How do you define 'real'?"

What is the true reason for 'The Matrix'?

Consciousness. Instead of harvesting energy (what Morpheus thought), the machines are cultivating humans for their minds, using them for skills they are unable to muster themselves: the ability to think and be creative.

In early years, a scientist who created the machines spent years trying to make give them the ability to think freely, but with no success. Eventually, he hooked himself into the machine, sharing his mind with the Artificial intelligence. This led to the AI's becoming super-intelligent, but only by sharing human consciousness.

More evidence to support this includes the bizarre fascination machines have with humans, and in particular the way they think. Although the machines may feel superior, they are fully aware that they couldn't exist with human input, hence the reason for The Matrix — to prevent humans from uprising against the machines by taking back control of their own minds.

The comment from #DeusExMachina, the central interface of Machine City, also backs this up, when it says: "We don't need you! We need nothing!" highlighting that they don't need humans to survive. Indeed without them, they would carry on, but they would lose the ability to think freely and wouldn't take on their own consciousness.