If you are seeking to read a defense of theism, you couldn't do much better than these two thoughtful, easy to read volumes by C.S. Lewis and Herman Wouk.
Mere Christianity
C.S. Lewis turned a series of radio talks into the compilation Mere Christianity (Harper, 2001, ISBN 0-06065-292-6). The book is perhaps the greatest modern case made in support of Christianity, and it addresses virtually every doubt and question either an atheist or a Christian may have. It follows an organized pattern beginning with the existence of morals, moving to the existence of a God, and eventually arguing that such a God came to earth in the form of a man, was crucified, and rose again. By using this slow build-up, Lewis avoids force-feeding Christianity to the reader.
This is My God
The Jewish equivalent of C.S. Lewis's Mere Christianity is Herman Wouk's This is My God (Back Bay Books, 1992, ISBN 0-31695-514-0). In it Wouk, like C.S. Lewis, uses a clear, conversational writing style, employing numerous analogies to make his points accessible. He offers a compelling apology for monotheism, which will be of interest to the Christian. The book is aimed at non-practicing Jews and gentiles who are "curious about the old Hebrew faith." The book is also very useful for the gentile who would like to know more about Judaism. It describes how and why the Jews celebrate the major holy days: Yom Kippur, Rosh Hashanah, Purim, Passover, Pentecost, Tabernacles, and Hanukkah. He talks about the diet of the Jews, their marriage customs, the rite of circumcision, and the bar mitzvah, among other things. He briefly discusses Judaism's perspective on the after-life and gives an overview of the major religious works: the Torah, Bible, Talmud, and Mishnah.