The man who's drunk water Knows if it's cool or warm.
If you put on a light, it's bright and you can see sick people, happy people, everything. Without light you can't see anything. The world is the same either way; it's only whether we have light or not that makes a difference. If it's dark, everyone is fighting each other and suffering. Everyone cries, "Where is the door? I want to go outside!" But with the light on, why would people fight? "Oh, there's a door here, a road there; one person can go here, another person can go out there."
How do we get out of this suffering ocean? With mind light. When it appears, you can go out the door and down the road. Mind light changes the suffering ocean into the dharma ocean. Everyone becomes harmonious, like happy children. Everyone gets true, unchanging happiness. Some people call this "pure light' or "nirvana." If you attach to nirvana, you will have a problem. But if you attain the correct function of nirvana, you can save all beings in this suffering ocean...
Each person's light by itself is very small. The stronger your practice, the brighter your light becomes. Putting everyone's light together means there will never be any hindrance. Together we multiply our light, and this dharma light is better than the sun. If a cloud appears, the sun cannot shine through it. Mind light has no such hindrance. If you see smoke, you know there's fire. If you see horns beyond the stone wall, you know there's an ox. That means your mind light can already see without hindrance.