According to the Scriptures, sacraments contain an outward or visible element. That is, sacraments are based upon material objects: water in baptism, bread and wine in the Supper. But a sacrament not only includes the material element prescribed in Scripture, but this also extends to the rite itself as commanded by Scripture. As we have seen, this language is used in connection with the Covenant made with Noah (Genesis 9:12-13), the covenant made with Abraham (Genesis 17:11); and as confirmed by Paul (Romans 4:11).http://www.christreformed.org/lecture-5a/