Ambrose of Milan (d. 397) composed his voluminous Commentary on Psalm 118 as a means to provide his audience, the Church of Milan, with a deeper formation, which would be a continuation of previously conferred mystagogical catechesis to the newly baptised immediately after their baptism. The Commentary on Psalm 118 is presented as a series of post-baptismal catecheses by the means of a personal interpretation of the Scripture in the context of the liturgical celebration of the Church of Milan as a kind of "profound" mystagogy and a help on the way to Christ.
The book comes to several conclusions. In his Commentary on Psalm 118, Ambrose presents a course of formation and catechesis that initiates his audience to the "school" of Christ, the Teacher.
It does not only transmit some teaching or practice, but it has even a purgative and redemptive value. By adapting the meaning of the Psalm 118, the assembly learned to know and to appreciate the presence of Christ in his Church and in the hearts of his faithful.
A special key to this process is Ambrose's idea of faith-trust that is opening between a Christian and Christ. The disciplina arcani is not only applied to the singular realities kept by the Church (Creed, Baptism, Eucharist and Our Father), but the Christian believer himself, his virtues, his spiritual reading of the Bible, his spiritual struggles and his "heart" become realities of the faith which are not to be spread easily but are to be kept as a treasure.
This view of man as a revelation of God's action and as a "sacrament" of God's mystery present in the Expositio is very original and modern. Ambrose succeeds in drawing his audience to the heart of theology, focusing on man in his life situation.
His figurative and symbolic language permits him to speak on God and his action that transcends human experience and possibilities of language, and so he promotes a meeting with transcendent God and his action in the present here and now. This approach, where theology, preaching and the real Christian life are brought together, remains very inspiring for the renewal of theology and for the pastoral care in any Church and in any time.