Crowley and Aziraphale are still unaware that the Antichrist was placed with the wrong family—they assume that the Dowlings’ son Warlock is the Antichrist, when really the Youngs’ son Adam is the true son of Satan. “The Arrangement” of placing Nanny Ashtoreth and Mr. Francis with the Antichrist (or who Crowley and Aziraphale
believe is the Antichrist) seems to be their way of assuring that Warlock gets a balance of good and evil in his life. Ashtoreth is a Pagan goddess—and Christians traditionally consider pagan worship to be idolatrous or sinful. Thus, having a nanny called Nanny Ashtoreth makes it clear that she’s the one responsible for giving Warlock his Satanic upbringing. Mr. Francis, meanwhile, is a nod to St. Francis of Assisi, the 12th-century founder of the Franciscan Order who was known for his love of all living creatures. It seems that he’s been sent as a counterpart to Ashtoreth, a benevolent presence to balance out her evil one. If Warlock is the true Antichrist (which readers know he isn’t), Crowley and Aziraphale seemingly want him to naturally fall into that role rather than being pressured or brainwashed into it—so they’re ensuring that his childhood role models are a balance of good and evil.