Mark 12:3

And they took him, and beat him, and sent him away empty. And again he sent unto them another servant; and him they wounded in the head, and handled shamefully. And he sent another; and him they killed: and many others; beating some, and killing some.

The many servants which the owner sent stand for the prophets of God, sent repeatedly to Israel, shamefully treated, and in some instances murdered. The Bible has many examples of this very type of treatment of the prophets. Isaiah and John the Baptist were both murdered; and practically all the prophets were rejected. In the sending of so many, and all of them receiving such treatment, this parable takes on the form of an allegory; because it would have been very unlikely that any earthly owner would so long have endured such rejection of his just claims, or that he would have sent a beloved son upon a mission so likely to be dangerous. However unlikely it may have been that any earthly owner would have thus persisted, this is, nevertheless, exactly the way God dealt with Israel and they with God. As Turlington said:

A parable is not bound absolutely by historical realism; it is bound by its purpose, however unusual its details. It is of course true that no father would be likely to send his son on so dangerous an errand.[5]