Oprah Winfrey

is gearing up for book release close to the media titan's heart. Winfrey will publish

What I Know for Sure

, a collection of monthly essays she has written for

O, The Oprah Magazine

since it debuted in 2004.

According to a press release, the book will focus on themes of possibility, joy and gratitude. The Mighty O based the title of her column on a conversation with late film critic

Gene Siskel.

The book is slated to hit stores Sept. 2.