Library Resources are arranged according the the Library of Congress Classification system. Once you know the general area where books on your topic are kept, it can be very effective to browse the shelves. How to read a call number
BT - Doctrinal Theology
10-1480 Doctrinal Theology.
19-30 Doctrine and Dogma
98-180 God
119-123 Holy Spirit, The Paraclete
198-590 Christology
695-748 Creation
750-810.2 Salvation
819-891 Eschatology
899-950 Future Life