"...Watch therefore, for you do not know what hour your Lord is coming..."
"....Watch therefore, for you do not know what hour your Lord is coming....But know this, that if the master of the house had known what hour the thief would come, he would have watched and not allowed his house to be broken into. Therefore you also be ready, for the Son of Man is coming at an hour you do not expect."
He said the we are to constantly be ready for the return of Jesus, for we know not of the hour nor day in which He returns. We are to continually ready ourselves as if today was the day of His return; to cleanse ourselves of all impurities, clean out all the unnecessary weights and sins that so easily beset us. This way we can be ready at anytime for His return and not be caught, in a sense, off guard. Just like our dog, who stood watch, expecting someone at any moment whether - or not we really were expecting someone or just doing daily chores. We keep clean, ready for our guest to arrive at any moment, as well as watching, anticipating the arrival of our Guest!