MQTT Broker and ChirpStack server

Hello !

I am working on a school project to try to create a private local LoRa architecture on my Linux PC for utilization of IoT devices in areas without internet connectivity. I have read about MQTT brokers such as MQTT Explorer and could not understand the relationship of it with the LoRa server. I have connected one sensor to the server and be able to see the uplinks. I was told that for me to decode the payload, I need to use Brokers like MQTT Explorer, then write scripts which will establish a connection to the MQTT Explorer and then decode the payloads whenever it detects a payload. Is the MQTT Broker is just and interface for my gateway or it has a connection to lora server. Since both can receive uplinks, why there is a need for MQTT Explorer and why can’t I directly decode the payloads from the server? Thanks.