In use from the earliest OT times as a means of authenticating documents and ensuring ownership. They were often made from small semi-precious stones, oval in shape, with a name carved on the seal so that when it was pressed in wax or clay, an impression remained. Letters were sealed (1 Kgs. 21: 8); a covenant was sealed (Neh. 9: 38); and a metaphorical use of sealing is used by Paul, who defined the circumcision of Abraham as a seal of the righteousness that he had by faith (Rom. 4: 11). Christians are sealed by the Holy Spirit (Eph. 1: 13). Christ is held to reflect the nature of God as closely as the impression made by a seal (Heb. 1: 3).