I read it like this: Why, if the wifi is 4.8Gbps, is the ethernet port only 1Gbps? How can the wifi serve 4.8Gbps if the WAN port is only 1Gbps?
The answer is that it can't. 4.8Gbps is the max theoretical speed anyway, and not the speed that you will see in reality. Your max internet speed will be limited by the 1Gbps ethernet port. Assuming you can achieve wifi speeds over 1Gbps, the only benefit will be that you can transfer data between wifi devices on the LAN at higher speeds than 1Gbps. If you want your wifi to have faster than 1Gbps internet access, then you will need to get a router and/or modem with faster than 1Gbps ethernet ports.