Russell’s major theme is the inexplicability of suffering and torment, especially that of those who trust in God and, from a specifically Christian standpoint, seek to propagate the faith. Each of the Earthlings is good-hearted and well-meaning, and Sandoz has been called a saint, a favorite of God; nevertheless, all die or suffer abominably or both. However, Russell steers clear of offering an easy explanation, though she explores a number of possibilities: suffering as a test of faith, sorrow as a conduit to closeness with the deity, the necessity of God’s absence to give humans space to exist as free beings. The most challenging possibility surfaces in a conversation between Fathers Giuliani and Reyes in the final chapter. Giuliani insists that God cares for his children, citing Matthew 10:29, the famous verse about God noting even the fall of a sparrow. Reyes points out God notes the sparrow’s calamity but wonders whether he merely observes. Does he care about the fall? This question brings up a possibility hinted at throughout the novel in the failure of the crew to understand the alien races they encounter: Perhaps God is so different, so essentially alien in comparison with humanity, that humans cannot perceive his actions and reactions, much less grasp his motives.
Another Christian theme expressed passionately in The Sparrow is the call to withhold judgment as found in Matthew 7:1: “Judge not, that ye be not judged.” The media as well as Sandoz’s own order are quick to express disgust at his apparent lapse into carnality and child murder. Yet, by the novel’s end, readers know that Sandoz is truly innocent: He fought his imprisonment and molestation, and the death of Askama was a tragic accident during a justifiable attempt at freedom.