Why did some of the new converts suspend their allegiance to the church when the seventh week in the “evil forest” approached?

Every Igbo village has an evil forest, where the undesirable dead and the powerful fetishes of medicine men are buried. The Evil Forest is believed to be full of malevolent and unpredictable magical energies. Everyone expects the Christians to die in a matter of days. When they remain alive, the people of Mbanto have to concede that the white priests command powerful magic. The Church begins to win a tiny number of converts.