"Mystagogy", simply put, is the study of mystery. For Christians, it focuses on the Paschal Mystery of the Lord Jesus Christ. It is an ancient and beloved Church method for reflecting on the experiences of worship, prayer, and the Christian life.
Here are booklets with reflections for the Collect and the Prayer after Communion for the seasons of the liturgical year. They are undated booklet that may be used over the years. The Table of Contents for each booklet is on the last page.
The individual reflections on the Collects and the Prayers after Communion in a single page format are accessible on the owner's website, the Federation of Diocesan Liturgical Commissions [FDLC] www.fdlc.org/mystagogical-reflections-texts-roman-missals-third-edition.