The term is not found in the New Testament, though the Vulgate sometimes uses sacramentum to render the Greek word for mystery (mystērion), as in Ephesians 1.19. The word may have been suggested by its secular meaning, the oath of allegiance taken by a Roman soldier on enlistment. The Roman governor Pliny (ca. 112 CE) described Christians as those who bound themselves by an oath (sacramentum) not to commit crimes.

By the third century CE, the word was being used to describe baptism and eucharist (see Lord's Supper) as specific acts of Christian worship, and it was later extended to include other official liturgical acts of the church. In 1564 the Council of Trent defined seven sacraments as instituted by Christ, namely, Baptism, Confirmation, Eucharist, Penance, Extreme Unction, Holy Orders, and Marriage. The Reformers with their biblical emphasis preferred to confine the term to baptism and eucharist, which are generally recognized as the two gospel sacraments.

The development of sacramental theology reflects different views found in the New Testament concerning the relation between God and human beings, where some stress God's grace and others faith. The Donatist controversy of the third century led to the use of the phrase ex opere operato to indicate that the efficacy and value of the sacrament did not depend on the worthiness of the minister but on the promise of God to the church. Therefore, as long as the church was obedient to its Lord and used the right “matter” (e.g., water in baptism, bread and wine at the eucharist) and the right “form” (the words or prayer expressing the meaning of the action), participants could be assured of God's presence and action in the sacrament. To avoid the mechanical understanding to which this view could easily lead, the Reformers emphasized faith in differing ways. Some, like Ulrich Zwingli, thought of the sacraments as signs of God's action in the past, whereas others regarded them as means of grace assured by the outward sign and the promise of Christ.

Modern theology tends to describe the sacraments as occasions of encounter between God and the believer, where the reality of God's gracious actions needs to be accepted in faith to effect a true meeting. This accords with New Testament teaching, which sees God's grace focused in the person of Jesus and his death and resurrection. This is the “mystery” of Christ (Col. 4.3), in the sense that God's secret purpose has been declared and made known in Christ. The sacraments therefore are means of grace insofar as they are occasions when the gracious act of God is made present to the believer. Paul expresses this understanding with regard to both the eucharist (1 Cor. 11.26) and baptism (Rom. 6.3–4).

The use of the term “the holy mysteries” (encouraged by 1 Cor. 4.1) to refer to the sacraments, especially in the Eastern Orthodox churches, shows more clearly the connection between the redemptive acts of Christ and their liturgical representation.

John N. Suggit