There a lot of books about the spirituality of St. Therese, and I'm not sure why. Since this saint and doctor of the church wrote during the late nineteenth century--indeed, she missed out on being a 20th century saint by only a few years--her writing is not at all difficult to get through. My own inclination is to skip the commentaries and just read Therese. (Today's Office of Readings give just one sample of her beautiful, ardent thoughts.)
But I'll make one exception. If you want a refresher on the Little Flower's teaching, yet are not in the mood to wade through her entire autobiography, you might want to try out I Believe in Love. This series of retreat conferences, translated from French, has been around since the 70s.
The author, Father Jean D'Elbee, takes you quickly into the heart and genius of Therese: her unique confidence in God's Love. A confidence that never fails, despite out sins, despite dryness and desolation, despite any suffering.
You can read I Believe in Love in a couple of sittings, or spread it out,say, with two chapters per day for a five-day, do-it-yourself retreat. This book has been a spiritual milestone for me, my husband, and many people that I know.
Great stuff to read during Eucharistic adoration.