Programs that want to receive or send data across the network do so using a port. A firewall (in the sense of a firewall on your computer) is basically a program that sits between the rest of your programs and your network connection and determines what programs should be allowed out to the network and what incoming connections should be allowed to talk to your programs.
This is “increasing security” by making sure you don’t let incoming connections talk to whatever happens to be running on your computer that might be listening for network traffic.
I can provide a more ELI5 explanation if you would like it.
The last time there was a major schism the nations of the day were explicitly aligned with one side of the other of the schism and the states attempted to crush the other side of the schism by force. Part of the separation of church and state in modern nations is meant to prevent church issues from becoming state issues (see the recent mainstream schism in the Methodist chuch which was completely peaceful and over similar issues).