Christian Formation is our mandate from Jesus himself to make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, and teaching to them everything that Christ has handed on to us (Matthew 28:19-20).
This is not merely for the accumulation of facts, but for the growth in holiness, “to help men believe that Jesus is the Son of God so that believing they might have life in his name, and to educate and instruct them in this life, thus building up the body of Christ.” (Catechism of the Catholic Church, 4) A life of formation in the Truth, sustained by the grace of God in prayer and the sacraments, serves to build up the believer, and indeed the whole Church, into the image of Christ.
Christian Formation also serves evangelism, as it empowers us to be able to give an account for the hope that is within us (I Peter 3:15). The Holy Spirit, the Spirit of Truth, promised to the Church to build it up in the teachings of Christ, also serves to transform the us into witnesses to Christ.