Faith without works is dead, but what is works without faith?
If the JWs had real faith they wouldn't need to continually push themselves into FS, they would be at it constantly. There would be people that had to be told slow down in the service because they were ignoring other important things. If you knew there was a million dollars buried in your backyard you would be out there digging every day till you found it. Nobody could stop you.
At best they think they are going to force fulfil God’s prophecy of the good news being preached to all the earth. They think by going door to door that they are fulfilling the prophecy. I can’t imagine it works that way. Do people generally know that they are actively fulfilling a prophecy or do they, or someone else figure it out after the fact? I’m not sure but I bet in most cases it is the latter.
It would be like the Jews saying, the bible says that a man named Jesus would be killed in fulfilment of some prophecy so lets find a guy name him Jesus and then kill him.