That refers to those who are being taught, and which flock only the faithful servant clearly belongs to, and obviously does not mean that all the examples used in this teaching that follows were saved. Give it up.
The Messiah warned those servants of the LORD being taught by calling them "Little flock" and listed the consequences if they did not do their reasonable service. Only one of three are expelled from His house when He returns from His wedding, to be with the unbelievers.
That servant, in whom the Messiah finds no fault, is made ruler over all His household. It seems incongruent to think of all the flock as the chief steward or even all the sheep as shepherds. It may refer to the question among the Apostles as to which of them would be given to sit at Messiah's right hand as ruler over all His house, whose house are we, if we hold fast the confidence and the rejoicing of the hope firm unto the end. We shall all pass before the judgement seat of King Messiah. Let us strive to do what He told us to do.