From ὑποκρίνω, to separate gradually; so of separating the truth from a mass of falsehood, and thence to subject to inquiry, and, as a result of this, to expound or interpret what is elicited. Then, to reply to inquiry, and so to answer on the stage, to speak in dialogue, to act. From this the transition is easy to assuming, feigning, playing a part. The hypocrite is, therefore, etymologically, an actor.
Against (ἔμπροσθεν)
Very graphic. The preposition means before, or in the face of. They shut the door in men's faces.