Why do we have crosses in church?

I've always wondered this: Why are crosses always displayed so predominately in church? Do we need some sort of image to remind us that Jesus died for our sins.

EXODUS 20:4 "You shall not make for yourself an idol [or graven image] in the form of anything in heaven above or on the earth beneath or in the waters below."

HEBREWS 12:2 "Let us fix our eyes on Jesus, the author and perfecter of our faith, who for the joy set before him endured the cross, scorning its shame, and sat down at the right hand of the throne of God."

The cross was the method used to torture of our Lord Jesus Christ. I understand that the cross that many wear (if you're not Catholic) is empty and has been said to celebrate the resurrection of Jesus rahter than some sort of worhsipping device. The cross itself is shameful and was used for killing.

Are we partaking in Idolatry to display a cross or wear a cross? Think about it. We don't need an image of the cross, an image of Jesus, or any other engraven image as the pagans did, or a Christmas Tree to remind us of Jesus and His gift to us.