Why you need an SWR meter

Hey guys, I just ordered a 500 watt 5ft Firestik antenna for my Cobra 19 Ultra 3 CB radio.

I talked with someone from Cobra and they said it does not matter how many Watts an antenna is, but you do need an SWR meter to set it up.

What if I dont have an SWR meter? Will the antenna still work?

Antenna for a handheld CB radio