What is the oldest sacrament?

Answer 1

The early church practiced two sacraments: Baptism and Lord's Supper (Eucharist). Both pre-date the formation of the church to some extent.

Baptism was practiced among Jewish proselytes before the time of Christ. John the Baptist carried out a similar sort of baptism... but one of repentance (rather like the Essenes).

The Lord's Supper was instituted at the Passover dinner between Jesus and His disciples before His death.

The book of Acts (and Romans) talks shows the early church practicing Baptism, while Paul's writings to the Corinthians shows that the Lord's Supper (with Love Feast) was practiced.

Some other actions like foot washing and anointing the sick were done, but they do not appear to have been treated as a necessary rite or sacrament within the early church.

Over the centuries, many more have been added. Roman Catholics have settled on seven. Orthodox have a different number. Most Protestants have held to the two original. However, some have none (such as Quakers and Salvation Army) while some others added (such as foot-washing). Many Protestants prefer the term "Ordinance" over the term "Sacrament". The term "Sacrament" suggests that the action is a purveyor of grace. "Ordinance" emphasizes its role (and limit) as a symbol.