I think it's awesome the way that the battlefields drive John for his ministry. He understands how thousands were on the "edge of eternity" in battle. Some went to heaven and some did not. With our salvation comes a great responsibility to lead those on the edge to salvation.
He stresses going to the uttermost parts of the earth. For John that doesn't just mean foreign nations, but reaching those that no one wants to touch.
Much of the battle that John fights is against the demonic forces and activities taking place in the Gettysburg area.
"sacrifice and consecration make an altar"
John believes that Gettysburg is/was the most powerful and passionate place of war in America.
He wants to use the Christian Commission and the museum as a platform for ministry; to spread the gospel as well as raise revenue to help others.
God doesn't ask us to do a favor...we are compelled to do so.