For anyone with questions about the concept of God and wishing to delve into theological matters, try Systematic Theology by Wolfhart Pannenberg (http://en.wikipedia.org/wiki/Pannenberg) (1988-1994, 3 volumes in the English translation published by William B. Eerdmans Publishing Company). This is an exhaustive analysis of all the key points in Christian doctrine. Required reading for Divinity students.
For a warm up try Theology: A Very Short Introduction (2000) by David Ford (http://www.amazon.co.uk/Theology-Very-Short-Introduction-Introductions/dp/0199679975/ref=sr_1_1?s=books&ie=UTF8&qid=1389547622&sr=1-1&keywords=theology+very+short+introduction)
Getting into your stride reach for The Cambridge Companion to Christian Doctrine (1997) edited by Colin E. Gunton (http://www.amazon.co.uk/Cambridge-Companion-Christian-Doctrine-Companions/dp/0521471184/ref=tmm_hrd_title_0?ie=UTF8&qid=1389547760&sr=1-10)
473 pages in William B. Eerdmans Publishing Company paperback edition
ISBN 978-0802865038
