Veneration of the Cross. This feast began in the 4th century after the miraculous discovery of the True Cross in Jerusalem by St. Helen. A traditional prayer for this is, "We adore you Jesus Christ and we bless you, because by your Holy Cross you have redeemed the world."
In the seventh century, the Church in Rome adopted the practice of Adoration of the Cross from the Church in Jerusalem, where a fragment of wood believed to be the Lord's cross had been venerated every year on Good Friday since the fourth century. According to tradition, a part of the Holy Cross was discovered by the mother of the emperor Constantine, St. Helen, on a pilgrimage to Jerusalem in 326. A fifth century account describes this service in Jerusalem. A coffer of gold-plated silver containing the wood of the cross was brought forward. The bishop placed the relic on the a table in the chapel of the Crucifixion and the faithful approached it, touching brow and eyes and lips to the wood as the priest said (as every priest has done ever since): 'Behold, the Wood of the Cross.'
Adoration or veneration of an image or representation of Christ's cross does not mean that we actually adore the material image, of course, but rather what it represents. In kneeling before the crucifix and kissing it we are paying the highest honor to our Lord's cross as the instrument of our salvation. Because the Cross is inseparable from His sacrifice, in reverencing His Cross we, in effect, adore Christ. Thus we affirm: 'We adore Thee, O Christ, and we bless Thee because by Thy Holy Cross Thou has Redeemed the World.