Contains practical, usable advice to help people who cannot enter a monastery or convent can grow in holiness where they are.
There are other great spiritual handbooks, but I don't think any of them are as accessible as this one.I agree! I can't say it any better than JMark does below, but I feel strongly enough about this book to echo some points.
I knew the book was a few hundred years old and was more or less expecting some datedness in the description of religious practice and in the writing style. What took me completely by surprise was how USEFUL de Sales' advice still remains. He was, as already mentioned, a gentle, wise and thankfully down-to-earth spiritual director. He did not expect over-night transformations and did not advise extreme measures in the spiritual journey. His writing is encouraging and immediately applicable.
When my husband was worried about dryness in prayer, I found the section in this book dealing with spiritual dryness and read it to him. He, although not much of a reader before then, immediately grabbed the book, read the section again himself, and told me that was exactly what he had been experiencing. He has taken permanent possession of the book (to my delight), and has gained a lot of reassurance and practical wisdom from it.
This is an excellent book for persons just embarking on a deeper spiritual life. Once you adjust to the vocabulary he uses, you will understand why Saint Francis de Sales was considered one of the best spiritual directors of his day, and is considered one of the Doctors of the Church. I wouldn't be surprised if, like so many other readers, you find yourself growing downright fond of him.