Why are relics significant?
It might be helpful to cite a recognized Church authority on the matter, (i.e., The Catechism of the Catholic Church (CCC) or perhaps The Code of Canon Law) to provide “legitimacy” to the answer to: “Why are relics significant?”
CCC No.1674: “The religious sense of the Christian people has always found expression in various forms of piety surrounding the Church’s sacramental life, such as the veneration of relics…” Also, regarding veneration, the CCC’s Glossary states, “Veneration must be clearly distinguished from adoration and worship, which are due to God alone.”
The Code of Canon Law: Can. 1186: “To foster the sanctification of the people of God, the Church commends to the special and filial reverence of the Christian faithful the Blessed Mary ever virgin, Mother of God, whom Christ established as the mother of all people, and promotes the true and authentic veneration of the other saints whose example instructs the Christian faithful and whose intercession sustains them.”