There are actually three roots of religiously themed exclamations: Invocations, oaths and curses. They all originate in the era when religion was almost universal. The invocation is an attempt to obtain the protective presence of the deity in the face of a challenging situation, such as when meeting something unexpected. “Oh my God!”, “Holy Mother of God!” “Saints preserve us!” and the originally quoted “Jesus Christ!” all fall in this category. They are generally an expression of overwhelm and surprise more than anything.
Oaths and curses, on the other hand, are used to strengthen one’s statements. The phrase “So help me God” is lifted right from courtroom oaths, and implies that if what I say is not true, God will stop helping me, a cruel fate in a world where the devil and his army roamed. In extreme cases one might even invoke the devil himself or the realm of hell as one’s destination if lying, basically cursing oneself. (This is a common source of profanity here in Norway, but less so in English.) A similar sentiment is found in the Old Testament, where an otherwise holy man swears: “God let it go badly with me both now and later if I …”
Over time, when a phrase is used so commonly that children grow up hearing it, they will acquire immunity and use it as simply a part of the language. And this is how even extreme scenarios like perdition have become part of casual speech in many western countries. I do not know how it is handled in other parts of the world though.
“Jesus….” when you narrowly avoid an accident?
My God, you scared me!”
Know in your heart what is said about the words you speak…
And we pray: