Religion isn't something World War Z spends a lot of time with, but it does raise a few religious queries here and there. Enter Father Sergei Ryzhkov.
Father Ryzhkov starts the war as a man of little faith. He provides infected soldiers with their last rites right before they are required to put pistol to head and kill themselves. Then one day, Father Ryzhkov feels the hand of God move him to kill the soldiers instead, claiming:
Suicide [is] a sin, and we, his servants—those who had chosen to be his shepherds upon the earth—[are] the only ones who should bear the cross of releasing trapped souls from infected bodies. (8.4.17).
This act prompts a religious fever that overtakes Russia. As a result, the country becomes a religious state, their president declares himself the head of the church, and rumors begin to swirl that he uses priests as political assassins. Silly? Sure it is, but it also elaborates a point World War Z is trying to make: politics and religion—especially extreme religious zeal—shouldn't mix.
We see a counterpoint take place in America during the zombie wars. Right-wing religious zealots think the zombie plague is sent to do God's will and try to kill the president (6.2.18). On the other end of the religious spectrum, left-wing religious extremists believe the zombies are doing Mother Earth a favor, and so "the Greenies" pour herbicide into some town water supplies as a type of ecoterrorism (6.2.22).
In both cases, the extremism of these religious organizations is countered and subdued by a government that separates itself form the church. No so in Russia, and the end product is disastrous for the freedoms and rights of the people.