In the Gospel of Matthew we find the Great Commission. Christ sends forth of the Apostles as missionaries with the command 

Go therefore and make disciples of all the nations, baptizing them in the name of the Father and the Son and the Holy Spirit” (Matt. 28:19; NASB)

Beginning with Our Lord’s earliest command that “all nations” be initiated into His Church and throughout the history of that Church that followed, it is natural that many coming to faith and entering the Church would be adults. Very early in Church history, therefore, there were established processes of instructing and ministering to adults as they journeyed toward baptism and the other sacraments. The term “catechumen” is used today to mean exactly what it meant in biblical times when St. Paul writes to the Galatians regarding “the one who is taught the word (Greek: catechumens)” (Gal. 6:6; NASB). Church Fathers St. Justin Martyr (2nd century A.D), Tertullian (3rd century A.D.), St. Augustine (5th century A.D), and many others reference periods of instruction and preparation for the Sacraments of Initiation (Baptism, the Holy Eucharist, and Confirmation) during the period known as the “catechumenate.” 

So, as the Catechism of the Catholic Church (CCC) tells us:

From the time of the apostles, becoming a Christian has been accomplished by a journey and initiation in several stages. This journey can be covered rapidly or slowly, but certain essential elements will always have to be present: proclamation of the Word, acceptance of the Gospel entailing conversion, profession of faith, Baptism itself, the outpouring of the Holy Spirit, and admission to Eucharistic communion.”[1]

The catechumenate was especially important and prominent in the early Church since, first, as previously mentioned, many (perhaps most) entered the Church for the first time as adults; and second, the early Church experienced several periods of severe persecution and it was critical that those entering the Church be well instructed in the faith for which they risked their lives. As time wore on infant baptism became more common and the persecution of Christians was lifted, the catechumenate appears to have received a bit less dedicated attention and development. That is not to say that it disappeared—as a missionary faith, the Church has always had some method of providing instruction and preparation for the sacraments. However, the conscious and focused development of a universal approach to the catechumenate faded somewhat following the Middle Ages.

The CCC acknowledges that the catechumenate was reinvigorated and RCIA established much later when “the second Vatican Council restored for the Latin Church "the catechumenate for adults, comprising several distinct steps." The rites for these stages are to be found in the Rite of Christian Initiation of Adults (RCIA).”[2] 

This initiative of Vatican 2 has resulted in the RCIA programs, the pathways into the Church for adults seeking after Our Lord, that we have in our parishes today.

More Information to Follow!!