This book is a classic. Written by the late Archbishop of Mexico City – who was a mystical theologian as well as a mystic and now a candidate for beatification – his treatment is grounded in the teaching of Saint Thomas Aquinas. It is magnificent but also accessible by readers who are not theologians.
The Sanctifier: Unabridged 2nd Edition by Archbiship Luis M. Martinez
In The Sanctifier, one of the most fascinating books on the Holy Spirit ever written, Archbishop Martinez reveals the secret of holiness. Step by step, he guides us to understand the gentle ways in which the Spirit acts in our lives. The author explains how the Spirit is present to us and leads us to the Father and the Son, especially through the virtues of faith, hope, and charity. He then focuses on the seven gifts, which make us attentive to the promptings of the Holy Spirit. Along with the gifts, we discover the consoling fruits of the Spirit, such as joy, peace, and patience. Finally, Martinez crowns his work with a masterful explanation of the beatitudes, the summit of the Christian life.
It is still in print but you should be able to find copies online, at least so you can see if you find the text to your liking before purchasing it.