First, welcome to the Straight Dope Message Board, japastor, glad to have you with us.
When you start a new thread, it’s helpful to others if you provide a link to the column upon which you are commenting. Yeah, it’s obvious today, when it’s on the front page, but in a few weeks, it will be buried amongst the thousands of other columns. So the link helps keep future readers on the same page, so to speak. I have edited your post to add that link. No biggie, you’ll know for next time.
OK, to your point. Cecil says: “…the Grail-as-mystical-object doesn’t appear in ancient Christian texts–unlike, say, the Ark of the Covenant.” I don’t see your problem. He’s not discussing the origin of the Ark of the Covenant, he’s describing the origin of the GRAIL. The Grail could not appear in pre-Christian texts, not under any remote fantasy, for obvious reasons. Thus, the earliest texts in which the Grail could appear would be “ancient Christian texts.” And Cecil is saying that the Grail doesn’t appear there.
However, ancient Christian texts DO mention the Ark of the Covenant – Letter to the Hebrews, specifically, is a Christian text that mentions the Ark of the Covenant. True enough, the Ark is mentioned in pre-Christian texts, such as the Hebrew Bible. But that’s not what Cecil is talking about. Cecil is saying that there are ancient “sacred objects” mentioned in ancient Christian texts, that the Ark of the Covenant is one such, and that the Grail isn’t.
In short, Cecil does NOT say what you’ve accused him of saying – he does NOT say that the Ark is “derived from” ancient Christian texts. He says it “appears” in ancient Christian texts, and there is a difference between “appears in” and “is derived from.”
Meanwhile, if you’d like to see the Straight Dope report on the Ark of the Covenant, its What happened to the Ark of the Covenant?. If you go to the part of our website called ARCHIVES and search on “Covenant”, you’ll find about four follow-up staff reports – a record to this day – and more than you’d ever want to know about the Ark of the Covenant.