The word 'relic' comes from the Latin "reliquae" (remains). Relics are grouped in three classes, ranging from actual body parts of the saint to items which have touched them.
In fact, the veneration of relics goes back to the Old Testament. We see evidence of this in a passage from 2 Kings 13:20-21. It records the death and burial of the great prophet Elisha and later gives an account of a dead man being cast into his grave. "When the man came in contact with the bones of Elisha, he came back to life and rose to his feet." This miraculous event occurred approximately six hundred years before the time of Christ. Similar veneration can be traced back to the New Testament as well. An example is found in Acts 19:11-12. So extraordinary were the mighty deeds God accomplished at the hands of Paul that when face cloths or aprons that touched his skin were applied to the sick, their diseases left them and the evil spirits came out of them.
History of veneration of relics
The early Church continued this veneration of relics. We read accounts from
Smyrna around the year 156, when St. Polycarp was burned at the stake. His
followers gathered his ashes and bones and venerated them with the greatest of
affection and respect.
So too did the friends and followers of St. Ignatius, Bishop of Antioch, who was devoured by lions in A.D. 107. Persecution of Christians was widespread throughout the Roman Empire, resulting in the deaths of thousands of martyrs. Some of them were buried in the catacombs in Rome. These burial sites became the prayerful destination of millions of pilgrims throughout the centuries. Following the legalization of Christianity by the Emperor Constantine in the year 313, basilicas and shrines were built above the tombs of the martyrs.
By the fourth century the practice of the veneration of relics had become widespread. So highly were these relics regarded by their owners that they were often encrusted with precious jewels and ornate metalwork. The custom has persisted throughout the history of the Church, and to this day, a relic of a martyr is placed on the altar of each new church. In his travels around the world, we see many instances where the late Holy Father, John Paul II, has prayed before the relics of a saint: we see photographs of him praying at the shrine of Lisieux, the burial place of St.Thérèse, and at Auschwitz, in the death chamber of St. Maximilian Kolbe. Shortly after his election as Pope on the feast of St. Charles Borromeo, his patron saint, he wrote, recalling his devotion to the saint: "St. Charles, how often I have knelt before his relics in Milan Cathedral."
Relics are venerated, not adored
While the custom of venerating relics may seem strange to the rationalist
believer or even to Protestants who, following Luther, rejected the Church's
sacramental system reducing religion pretty much to the reading of the Bible,
for the Catholic Christian it seems the most normal and logical consequence of
the Faith.
The Church has always respected and encouraged the custom of expressing veneration for the remains of our loved ones, particularly the saints, our models in spiritual life. They are the ones who can teach us how to live closer to God. God has frequently exhibited His approval of the use of relics in the Church by working miracles through them. The bodies of the saints (like our bodies) are "temples of the Holy Spirit" (1 Cor 6:19) and are the instruments through which God performs some of His mighty works. Thus it is only fitting that the Church encourages us to treat the remains of the saints with the utmost love and respect; never adoration, however, for adoration is fitting only for God. That indeed would be idolatry.
We pray to these saints as those who are closest to God, that they may carry our prayers to Him.