I know this is old news, but just found this priceless quote on jwfacts from 2001 watchtower (yes 2001 not 1941!!!) looks like Geoffrey Jackson never read this one:
"Is it presumptuous of Jehovah's Witnesses to point out that they alone have God's backing? Actually, no more so than when the Israelites in Egypt claimed to have God's backing in spite of the Egyptians' belief, or when the first-century Christians claimed to have God's backing to the exclusion of Jewish religionists." Watchtower 2001 Jun 1 p.16