Learn English – What’s another phrase for….pushed to the limits? going through great adversity

I believe that Edwards is saying that God still has work for Edwards to do - presumably something to help children “in the poorest parts of this country.”

However, the phrase can also be construed to mean that Edwards is not a finished product - that God still has some work left to do on him to make him a better person. Many years ago at Vacation Bible School, I learned a little song:

We're kids under construction
Maybe the paint is still wet
We're kids under construction
The Lord might not be finished yet.

I can't answer your question about acceptance in countries/regions other than the US - but I can tell you that through with x is a widely-used construction in the US; it can mean

• finished using: Are you through with that wrench yet?
• finished working on: Are you through with your homework yet?
• disgusted with/tired of: I'm through with love. (Marilyn Monroe, Through With Love)
• terminating a relationship with: Jane says "I'm through with Sergio - He treat me like a rag doll" (Jane's Addiction, Jane Says)

There's also a closely-related (but not identical) idiom when I get through with x, which can mean:
- when I've finished working: I'll call you when I get through with my report.
- when I'm done beating/punishing (a person): When I get through with you, you'll wish you'd never been born.
- an ironic positive usage, based on the previous: You think you love Sue, but when I get through with you, you won't ever look at Sue again. (Patsy Cline, When I Get Through With You You'll Love Me True)

Finally, there is a similar but unrelated phrase to get through, meaning to arrive at a destination despite obstacles or interference: The message got through at last. If it's a messenger or a courier who arrives, s/he might be carrying something, and one might say that s/he "got through with" it: Balto and his team got through with the diphtheria antitoxin just in time. Again, however, this is an unrelated usage.

"Down to the word" and other constructions like it (usually you hear "down to the letter") simply refers to the sameness of one thing with respect to another. What it asks you to do is to consider the detail mentioned, not whatever standard of sameness you may normally be tempted to apply.

Consider two identical twin girls: you could say both are human beings. You could also say they are both female, both are the same height, the same weight, the same age (give or take a few minutes), the same race, etc. But instead of these coarse comparisons, you could emphasize how alike they are by saying

They are alike down to their facial features.

The idea of "down" in this sense calls to mind going from broad comparatives down to finer and finer ones — ultimately to whatever level of granularity is specified. If one oral presentation, such as a speech, is like another "down to the word" it is identical at that level. If it is a written document (one student's homework is identical to another's, say) it could be said to be the same down to the letter, or down to the line breaks, or whatever metric you wish to apply.

Imagine viewing something from the top of a building. You would have to go down closer to view the details. That is the sense of it: zooming in to consider minute details.