In this story, Marquez is satirizing the shortcomings that prevent humans from being able to adequately show religious faith and reverence in the face of the divine.
Most pointedly, Marquez mocks the Catholic Church. When notified by Father Gonzaga of the possibility that a genuine angel is being imprisoned and...
mistreated by villagers, Church officials in Rome do not rush to the village to ascertain the supposed angel's identity, administer aid, or discourage the villagers from their abuse. Instead, they waste time writing letters that pose esoteric questions about how angels are "supposed" to be (for instance, whether the angel has a belly button). In fact, the Church officials ask "how many times he could fit on the head of a pin"—a philosophical question usually invoked to describe a useless concern with irrelevant details. The Church is unable to access genuine faith because it is caught up in useless minutiae. The Church's rigidity and doctrinaire approach prevent the officials from recognizing a miracle or from doing anything to help one of God's creatures.
The villagers' faith is quicker; Pelayo, Elisenda, the neighbor woman, and a number of the villagers readily accept that the old man is an angel. However, their religion is greedy and self-serving, and they lack appropriate compassion and respect for the angel. Pelayo and Elisenda imprison the angel and charge admission to see him, caring only for their profits instead of the angel's comfort or dignity. The villagers see him as a carnival attraction instead of treating him with religious reverence and are easily distracted when a more interesting sideshow comes to town. They prefer this false idol (the spider with a girl's face) because it is more accessible and its stories are easier to understand. Marquez insinuates that humans are too fickle, impatient, and self-interested to gain a deeper religious understanding than their own material interests dictate.