Why Shouldn't We Wear a Cross as a Sign of Being a Christian?
Having a desire to let our light shine and to share our faith are positive goals! In order to answer this specific question, though, we must also consider the background of the cross, the New Testament record and Jesus' teaching about how to display our Christianity.
One of the first questions we might ask is, Who decided that the cross was to be the sign of Christianity? This tradition of wearing a cross does not come from the Bible or the practices of the New Testament Church. Though there are at least seven different types of crosses, we are not even certain that Jesus was crucified on a cross-like apparatus. Though crucifixion on a cross was common at the time, the Bible allows that Jesus may have been put to death on an upright pole (rendered "tree" in 1 Peter 2:24 from the Greek word stauros, which primarily means an upright stake).
A study of history shows that the cross symbol predates Christianity. According to author Ralph Woodrow, "Centuries before the Christian era, the cross was honored as a religious symbol by the people of Babylon. It is seen on their oldest monuments. Historians say that it was a symbol associated with Tammuz" (Babylonian Mystery Religion, p. 51). From Babylon, the cross spread to other nations and was associated with paganism long before Jesus' crucifixion in A.D. 31.
Woodrow further explains, "It was not until Christianity began to be paganized that the cross came to be thought of as a Christian symbol. It was in 431 A.D. that crosses in churches and chambers were introduced, while the use of crosses on steeples did not come until about 586 A.D." (p. 50).
While most people today connect the cross with Christianity rather than paganism, we must also ask if the cross is something to be worshipped or honored. While the apostles preached "the cross [stauros]" as part of the history of Christ's ministry for our sakes (1 Corinthians 1:17-18), it was not something they idolized. It was a shameful instrument of death (Hebrews 12:2). In His crucifixion, Jesus took on Himself our shameful sins. Having our sins forgiven is a wonderful blessing, but there is no need to glorify the instrument used.
Finally, consider what the Bible teaches about wearing any religious symbol. Under the Old Covenant that God made with ancient Israel, God instructed them to wear reminders of their faith upon their hands (Deuteronomy 6:8; Deuteronomy 11:18). In fulfillment of this command, phylacteries, small leather boxes containing scriptural passages, were traditionally worn by Jewish men during their morning weekday prayers. Many did this to appear righteous to others (Matthew 23:5).
During His New Testament ministry, Jesus taught His followers to display their spirituality through their actions and deeds (Matthew 5:16). Under the New Covenant, ushered in by Christ, God's laws are to be written on our hearts—that is, in our minds (Hebrews 8:10; Hebrews 10:16). People who truly practice the Christianity of the Bible stand out as beacons of light in a spiritually darkened society because of the way they live. They have no need to wear external signs like a cross to identify themselves as Christian.
If you would like to learn more about the history of the cross and how this pagan symbol entered Christianity, read chapters 6 and 7 of Ralph Woodrow's book, Babylon Mystery Religion. These two chapters are respectively titled "Is the Cross a Christian Symbol?" and "Constantine and the Cross."