My guess... "encrypted" regarding router will refer to a WiFi router, where STRONG encryption is an absolute necessity to ensure your WiFi isn't subject to exploitation by wardrivers, malicious neighbors, curious script kiddies, and so on.
Most hardware firewalls such as are commonly found in consumer-grade routers are SPI (stateful packet inspection); meaning that they examine each inbound packet to see if it's in response to a previous outbound packet, and check packet integrity to make sure they are what they say they are.
The NAT functionality (also common to these devices) simply means that on your side of the router is a different IP address than on the world's side. So the world sees the IP address assigned by your ISP; your computer has a different, non-routable IP address (ie, only usable across a network, rather than the internet). Thus if you open a command prompt and type "ipconfig /all" (no quotes) you will see that the IP address for your computer is different (typically 192.168.x.x) than what you get if you go to
www.whatismyip.com (or just look in the lower right corner of your posts here).
As has been pointed out in the thread that sded linked, IMO you need both. They serve different functions, and in different ways.
BTW, CFP also has a powerful SPI engine built in.
LM