The reason Christ's body is on a catholic crucifix is an acknowledgment of suffering in this world. Christ suffered, and He has asked us and expects us to take up our crosses as He took up His. Suffering did not end because He rose. He is with us in our sufferings, and seeing His body on the cross reminds us of that as well. There is no suffering that He can't understand, because He experienced it all.
Once again (I've written this before in other posts), images used in catholic churches, like crucifixes and statues of saints or stained glass windows, etc. are *not* worshiped!!!. They do *aid* worship, but they are not worshiped themselves. Having statues of saints, for example, is a lot like having pictures of loved ones in one's home. Do you love the pictures, or do you love your loved ones? If you don't love the pictures themselves, then why bother having the pictures? Because they are loving reminders of those whom you love, aren't they? As I said, with the crucifix, it reminds us of the concepts that Our Lord suffered - and continues to suffer in His heart - pain from our sin, that human existence contains suffering, and that He is with us in our suffering especially because He experienced it firsthand.
Michael, the Archangel, defend us in battle. Mary, Our Mother, protect us under your mantle.