"The heart is the real battleground during suffering, and it deserves your utmost attention" (190). This is one of the convictions that lies behind this book, where Welch is particularly concerned with "listening to depression," and then responding with gospel truth. In the central section of the book, he explores the thoughts and heart attitudes that are thrown up when depression of all kinds comes upon Christian believers. As such, this isn't just a book for those with diagnosed clinical depression; other believers would benefit from Welch's insights.
At the same time, I would be cautious about recommending this to someone with moderate to severe depression. It's quite an intense read, at a point where someone might not want to read at all! It is particularly intense because, contrary to the title, a lot of the book encourages readers to "look in", which could produce unhelpful introspection for some - and a few of Welch's remarks could easily be misheard by a depressive mind. I would also take issue with some of Welsh's reservations about medication and non-Christian treatments.
Even so, if you're a depressed Christian looking for something good to read, you might still want this book. And the best way to use it would probably be to go through it slowly with a trusted friend, when the mental storm is not raging quite as much. In the process, you will learn a lot more about yourself - and you'll be reminded to look to the Lord, however dark things get.