As you may know, "Christ" means anointed, or Messiah, not God. Thus, "mother of Christ" doesn't assign Jesus the proper position that He is - God. I do not recall in the Old Testament that makes the connection obvious that the Messiah would be God Himself. Thus, the early Christians would want to make it clear that Jesus was God - and they did so, among other means, by naming Mary the Mother of God.
As to "mother of the Second Person of the Trinity", that is a bit unwieldy, don't you think?
Finally, why on earth are you making such a big deal out of this? Do you enjoy arguing with others?
Regards
That's hairsplitting in today's world. Many/most of the lost know that we say Christ is God. But if you're talking about early Christian witnesses, it would seem to me that the ultimate blasphemy (to a lost person's ears) would be to use a term like "mother of God", implying Mary's preexistence. You cannot possibly tell me than an early lost person wouldn't take it that way. It would require a full explanation, no less so than "mother of Christ" would require to the same audience. The Jews went nuts at the thought of Jesus being God. On the same surface it would be the same for mother of God.
Finally, why on earth are you making such a big deal out of this? Do you enjoy arguing with others?
Actually, the tale of the tape on this thread would show that I have not been one to make a federal case of this. I have made several comments, but I have not been one to scream bloody murder. I have said Theotokos is fine with a full explanation. I would just use other terms first in witnessing. This isn't an I'm right/you're wrong issue for me like so many are. :) I just have some concern that Mary could be seen by the lost as being something she was not.
And of course I enjoy arguing with others. I'm a lawyer. :) I only hope that those with whom I have had these conversations have found it as enjoyable, educational, and beneficial as I have.