Luke 12:36

“And be you yourselves like to men looking for their lord, when he shall return from the marriage feast, that, when he comes and knocks, they may open to him straight away.”

And the servants themselves had to be like men who were waiting for the return of their lord who could arrive at any moment. He had gone to a marriage feast (which would be of uncertain length), but all must be ready for his return, and when he did arrive and knock things had to be in such a state of readiness that they could open the door immediately. The picture is one of conscientiousness, bustle and preparation, and of all efforts being expended in one direction only, readiness for their lord's return so that everything was perfect in the household when he came.