Relics go back to quite ancient times, even to the Old Testament when there was reverence for the “bones of Elisha.” 2 Kings 13:21 Once while some Israelites were burying a man, suddenly they saw a band of raiders; so they threw the man’s body into Elisha’s tomb. When the body touched Elisha’s bones, the man came to life and stood up on his feet.In the New Testament, second class relics of Paul do the same:Acts 19:12 so that even handkerchiefs and aprons that had touched [Paul] were taken to the sick, and their illnesses were cured and the evil spirits left them.There are a number of miraculous accounts associated with the relics of a holy person. The early Church was diligent, as I understand, in preserving the bones of the Apostles and other holy saints. You could look at it as sort of a reflection of the incarnation of Christ. Christ, having become incarnate, entered this world not only spiritually, but physically. It is a sign that the body and spirit are united in a single person. Any miracle, or even just any prayerful attitude inspired by the relics, is a sign that Christ came incarnate and truly makes us holy. It is something we can see that fortifies the faith.