A HomeKit bridge allows you to integrate your Home Assistant entities into Apple HomeKit. This allows you to control your Home Assistant devices through the Apple Home app and Siri, even if those devices do not naturally support HomeKit. The HomeKit bridge essentially acts as a translator between the two platforms, making your Home Assistant entities accessible and controllable within the Apple ecosystem. By using a HomeKit bridge, you can enjoy the convenience of controlling your smart devices through Apple's intuitive interface and voice commands via Siri.