From the Latin ‘sacramentum’, meaning an oath, as taken by men joining the Roman army. Already by the time of the governor Pliny (112 CE) the term is used of Christian practices—he misunderstood their sacraments to be oaths by which they promised not to commit crimes. The Latin Vulgate translated the Greek mysterion by sacramentum, which led to Baptism and Eucharist being designated sacraments. Other rites were added to these sacraments by the mediaeval Church, but the Reformers restricted the number to the two explicitly mentioned in the NT (Matt. 28: 19 and 1 Cor. 11: 23–5). The biblical references to other rites such as confirmation are less clear.

It is generally held that in the Church baptism corresponds to the OT rite of initiation (circumcision), and Eucharist is related to the OT festival of redemption, Passover.