A sacrament is a visible manifestation of the word. The bread and wine in the Lord's Supper are considered sacraments in that they are visible manifestations of the covenant promise of our Lord: "In the same way, after the supper he took the cup, saying, 'This cup is the new covenant in my blood, which is poured out for you,'" (Luke 22:20).
God, in the Old Testament, used visible signs along with His spoken word. These visible signs, then, were considered to have significance. Among the OT sacraments, the rites of circumcision and the Passover were stressed as being the OT counterparts of baptism (Col. 1:10-12) and the Lord's Supper (1 Cor. 5:7).