I cut the ground wire on my chandelier before knowing what it was. What do I do?
Metal parts of luminaires are required by the National Electrical Code to be grounded. This is for safety in case the "hot" wire contacts the metal of the luminaire and it becomes energized, the ground wire will complete the circuit and cause enough current to flow to trip the breaker.

Chain hung luminaires accomplish grounding by weaving a small bare wire through the chain to the luminaire. If you cut the wire the luminaire will work normally except in the case I mentioned above. In that case the metal of the luminaire is now energized but the breaker does not trip because there is no return path. Until someone touches the metal part of the fixture and touches a grounded object at the same time. This then completes the path through the person with disastrous results.

In residential settings there not as many grounded objects as in industrial and commercial locations. However, safety is of prime concern so the requirement for grounding metal luminaires now applies in all settings.

So, you could splice the wire with a butt splice, although this would not be very attractive.

Or, you could replace the wire with a new piece of bare copper wire. Luminaires usually have a #16 to 20 gauge wire as the ground. If you can't find anything smaller a bare piece of #14 copper will do just fine.

Good luck and stay safe!