Although I have not read as much of his writings as I would like, I am a very big fan of St John of the Cross as a master and guide on the spiritual life.
In some of my previous posts you may notice there is a theme of silence or solitude, this is due to my existentialist leanings. They are also very predominant themes in St John of the Cross as well
“Whenever anything disagreeable or displeasing happens to you, remember Christ crucified and be silent.”
St. John of the Cross