Exo 20:24 An altar of earth thou shalt make unto me, and shalt sacrifice thereon thy burnt offerings, and thy peace offerings, thy sheep, and thine oxen: in all places where I record my name I will come unto thee, and I will bless thee. 25 And if thou wilt make me an altar of stone, thou shalt not build it of hewn stone: for if thou lift up thy tool upon it, thou hast polluted it.
In verse 24 God instructs Moses to make an altar of earth. The Hebrew word translated "earth" is from the root adam which means "to show blood, be red, ruddy." Adam is also the root of the word translated "man" in Genesis. So when Paul, in Romans 12:1, says, "I beseech you therefore, brethren, by the mercies of God, that ye present your bodies a living sacrifice, holy, acceptable unto God, which is your reasonable service." he is telling them, in essence, to make themselves into an altar of earth, to sacrifice their self-centeredness to God. And God, in Exodus, promises to bless them if they do.
Then in verse 25 God speaks of an altar of stone. The Hebrew word here is eben, which is nearly identical with the word for son, ben. This is an allusion to Jesus the Son (ben) of God, who is often represented by a stone or rock in Scripture. God is saying to us that if we trust in Jesus but try to change Him at all, chipping some off because we don't like it, or adding our work to His, then we have polluted it. We cannot be saved by our own work, but only by the work Jesus did during His death, burial, and resurrection.