P.O. Box B as it Relates to Isaac's Mission

I just read a book of short vignettes by President Boyd K. Packer, "Memorable Stories with a Message."  One of the stories, P.O. Box B talked about receiving a mission call.  One of the stories cited was a missionary call extended the same year Isaac Wardle was serving his mission.  I think the attitude may also reflect Isaac's.  I know from reading his letters, Isaac had a sense of pride in being called and deemed worthy to go on a mission.

"I have a letter signed by President John Taylor, written on April 12, 1884.  It has an interesting letterhead:
The President’s Office
The Church of Jesus Christ of Latter-day Saints
P.O. Box B
Salt Lake City, UtahP.O. Box B” became the symbol of the mission call for generations of Latter-day Saints.  A letter from Box B was a call to the mission field.  Those letters cam unannounced: no interviews, no asking whether it was convenient—just a letter from Box B, a call to serve.  
Here is a response addressed to Box B, datelined Beaver, Utah, August 30, 1879,
'President John Taylor
Dear Brother,
Yours of the 27 instance notifying myself to make my arrangements to go on a mission to the United States is to hand.  You ask an answer of me.  My answer is, I am glad that I am counted worth by my brethren to go on a mission or fill any place of trust and I hope that I shall never do anything to forfeit the confidence reposed.
I know of nothing now to prevent my going as desired although plenty to do at home.'
That simple phrase although plenty to do at home no doubt referred to a wife and family to feed and clothe, children to teach, a farm to keep, cows to milk, a garden to tend, a home to complete.  All were set aside because a letter had come from Box B.
…Wiliam W. Phelps wrote:

I go devoted to His cause,
And to His will resigned;
His presence will supply the loss
Of all I leave behind.

I go because the Master calls;
He’s made my duty plain—
No danger can the heart appall
When Jesus stoops to reign.

Perhaps a few refused the call from Box B, but we have no record of them.
Much has changed since those Box B days, but one thing must not change.  We must not—we cannot—lose the spirit of the call, for it is a demonstration of the power of revelation."