Could you explain the moral difference between drama and oratorio? 

Maybe I should explain my question. I've sung in several oratorios which required the chorus to sing an evil crowd chorus (e.g., "Let Him deliver Him" in Handel's Messiah, "Baal, We Cry to Thee" in Mendelssohn's Elijah, and "Crucify" from Bach's Passion According to St. John. Such choruses hold essential meaning for the overall message, but they require the singer to imitate evil. (I have the same dilemma regarding effective story telling or even Bible reading.) It seems necessary, but it seems to have that same element of wrongness as other drama (overacting). Can you explain it? I'd be grateful.

Let me say at the outset that I can appreciate your disapproval of drama, your antipathy toward it, and even your dilemma in singing in an oratorio that expresses evil. Personally I have a strong dislike for anything that resembles playing or acting out that which is sacred, or that which is sinful. We can well be aware of this in a time of spiritual lukewarmness or indifference. 

Yet it must be granted that there is a definite difference between drama and oratorio from an ethical point of view. 

Drama is defined in Webster's Dictionary as, "A composition, now usually in prose, arranged for enactment, and intended to portray life and character, or to tell a story by actions, and, usually, dialogue, tending toward some results based upon them; a play." 

The key word is enactment, i.e., a "playing the part of." The actor places himself in the situation of another individual, either imaginary or real, pretending to be that person and taking his place in certain experiences. 

Therefore, to be a successful actor he must be able to enter into the thoughts and feelings of the individual he is enacting, or impersonating. For in the minds of the audience that actor must be so completely associated with the real person, as if he were that person. The actor and the audience must be able to put heart and soul into that experience in order really to enjoy it. 

It is exactly at this point that the evil of drama becomes evident. This hardly needs to be shown. For example, when the life of Luther is acted out on the stage his personal spiritual struggles and prayers are also acted out. Does the actor actually experience the same soul-struggles? Are his prayers divinely acceptable? Of course not! And that means that his acting is nothing short of blasphemy. How about the audience? Should they show reverence during such a prayer by folding their hands and closing their eyes? Or should they stare at the scene in indifference? In any case it would be sacrilege to participate in such evils. 

This would also be our objection to any sort of Passion Play. 

On the other hand, when the actor relives the sinful deeds of another he is placing himself in that sinful situation. Can he do that without sinning? Can he, for example, enact a love scene and remain coldly indifferent? The successful actor takes his audience along with him, so that they also experience the same sinful emotions that accompany the deed. They sin vicariously, often even making themselves guilty of sins they would be ashamed to commit. 

We do well to give this our serious consideration, especially as we live in the midst of a godless world, in which God is no longer recognized, God's law is violently trodden under foot, and sin is no longer regarded as sin! 

The question is, Is oratorio the same as drama? Does the choir actually involve itself in the contempt and hatred expressed by the angry mob that cries out, "Crucify!"? Or does the choir carry the audience along in actually joining the Baal worshipers who are seeking help from Baal? The difference is obvious. There is a definite difference between impersonation and imitation, or portrayal. While drama is definitely impersonation, involving heart and mind, imitation merely places strong emphasis upon a certain act or speech. The singer is not at all in agreement with the crowd, but is strongly opposed to them, when taking their evil words upon his lips. The one who portrays another makes no effort to pretend to be that other person. 

It must be admitted that portrayal can readily become impersonation. When one reads a novel, even a "Christian" novel, one can become so involved with one of the characters, that he becomes guilty of the sins that are described in the story. We can allow ourselves to be carried along to the extent that we become guilty by substitution, that is, allowing ourselves to become guilty of the sins portrayed in the book. 

The same thing applies to story telling and Bible reading. The evils that are recounted in the Scriptures are placed there for our instruction and admonition, and must be read with a great aversion to sin, as well as with a deep consciousness of our own depravity. In telling these stories to children the same reaction should be sought in them. On the other hand, there is an intimate bond of communion with the saints of Scripture when they cry out in the midst of their trials and temptations, confess their sins, express their joy of salvation, and give praise to the God of our salvation in worship and adoration.

The admonition of Scripture comes to mind, 

Be ye followers (imitators) of God, as dear children; and walk in love, as Christ also hath loved us, and hath given himself for us an offering and a sacrifice to God for a sweet smelling savor. But fornication, and all uncleanness, or covetousness, let it not be once named among you, as becometh saints; neither filthiness, nor foolish talking, nor jesting, which are not convenient: but rather giving of thanks. Ephesians 5:1-4