The Reason for Existence

Humans exist because God desired more children.  Deification, divinization, or divine filiation are all names for the process by which the divine life and love is restored in us through prayer, the sacraments, Scripture reading and meditation, works of mercy, and the whole Christian life in the Spirit.  God loves us--that is why we are here.  We fell--that is why we are in such a mess.  Divine love entails utter self-gift, which human nature experiences as utter self-sacrifice--that is why we are called to suffer and die.  For more on how all this works, see this excellent overview. 
Excerpts:

...In my opinion, if the would-be director is not familiar with the content in the first three books they should pause their spiritual direction practice and dig in. Beyond these books, the rest are great resources in the areas of prayer, discernment, holiness, and spiritual direction. As well, anyone seeking to better know, love, and serve God would be blessed by all of these works, particularly items two through ten.

1. Guidance in Spiritual Direction by Fr. Charles Hugo Doyle: This book is specifically written for clergy and very clearly outlines the necessary perspectives in insights for a priest looking to provide sound spiritual direction. Though it is written for priests, tt would also be very helpful for anyone who provides spiritual direction.
2. The Three Ages of the Interior Life by Fr. Reginald Garrigou-Lagrange: This is a classic and is, in my opinion, the most thorough of all systematic treatments of the topic.
3. The Spiritual Life by Fr. Adolphe Tanquerey
4. Spiritual Theology by Fr. Jordan Aumann
5. Discernment of Spirits by Fr. Timothy Gallagher
6. The Fire Within by Fr. Thomas Dubay: This book will help the reader gain proper perspectives on prayer and avoid common misdirection and misinterpretation of Saints Teresa of Avila and John of the Cross.
7. The Fulfillment of All Desire by Ralph Martin
8. Seeking Spiritual Direction by Fr. Thomas Dubay
9. Anything by St. Teresa of Avila – particularly The Interior Castle, or St. John of the Cross
   
10. Introduction to the Devout Life by St. Francis de Sales

Regarding common modern issues with misdirection in prayer, Cardinal Ratzinger (now Pope Benedict XVI) wrote this “Letter to the Bishops of the Catholic Church on Some Aspects of Christian Meditation....”

This is the heart of life, the meaning of existence, the path towards peace--progress along the spiritual path towards the communion with the Trinity that God desires. God bless, all who read this! God bless, all on the way! Pray for me, that I have the courage and fidelity to walk this path, as well!