If you orient the entire week toward the sabbath and are consistently engaged in private worship, this preparedness for public worship falls naturally into place. However, circumstances in life -- young children in the home, working in emergency or military settings -- can interfere greatly with being prepared. In that case, I'd say it's the adversary who prods and says: but you shouldn't worship, look how unprepared you are!
I have always appreciated the Lord's mercy in allowing me to worship him. It is a great thing to meditate on the privilege and duty of corporate worship. I am always blessed that the Lord transcends (I am not sure if that if the appropriate word) when he allows a wrench like me to worship him. Thanks for the great quote, it is a good reminder of what we do is serious business.