This is even more confusing now, because on one hand I have people telling me that the sentences are ridiculous, but on the other I have people I respect and trust telling me otherwise.
English is not my mother tongue, and I am well aware of my limitations, but I have seen (or read, or heard) "behold" many times, although always in contemporary English. I don't think that "He aquí" sounds as archaic as "behold" sounds in those examples, since you are likely to come across "he aquí" almost every day if you read newspapers and other printed text.
Still, (and I apologize for being so annoying) I don't think I can capture the real meaning of "behold" in those sentences. Let's take James' detailed example (the most useful one so far):
- So, you are trying to get that promotion'(Feigning an evil villian's voice) - Yes, my plan for corporate domination is coming along nicely. - I heard that Smith won't be trying for that job. - Behold my opportunity!
Can anyone give me a contemporary equivalent sentence for that "behold" one?
To me, that "behold my opportunity" seems to be clearly directed at the other guy, as if you were saying: "Just look and don't miss what's about to happen". Maybe I have the wrong idea, but to me, this "behold" always sounds like "Look at wonder", "Look at don't miss any detail" or something else to call for other people's attention. On the other hand, "He aquí" to me means, no more, and no less than "Aquí está", but more formal. Taking it to extreme, you could be alone, without anyone listening to what you say, and then, all of a sudden, you find something you lost some time ago, and then you say to yourself: "¡Hombre, he aquí mi [lost object]". This means, no more and no less, "Oh, here it is my [whatever]". Is this really what "behold" used to be about? (I won't ask any more, don't worry).
A contemporary equivalent: Oh look, there are my glasses!
As has been said on this thread before, the basic meaning of "behold" was "look", but it also came to be used as an exclamation, basically "Hey!!" (in American slang) -- a verbal cue to take notice. Here is a quote from "A Midsummer Night's Dream:"
Or, if there were a sympathy in choice,
War, death, or sickness did lay siege to it,
Making it momentany as a sound,
Swift as a shadow, short as any dream;
Brief as the lightning in the collied night,
That, in a spleen, unfolds both heaven and earth,
And ere a man hath power to say 'Behold!'
The jaws of darkness do devour it up:
So quick bright things come to confusion.
You can see more here Shakespeare quotes here (this might be your best bet, since none of us, native speakers or no, are actually Shakespearean contemporaries).