TWU uses two forms of classification for books. The main one is Library of Congress (LC) and all the call numbers on these books start with letters.
The other system (Dewey Decimal) starts with numbers and is found on books that came into the library from the Northwest Baptist Theological College Library. Dewey books are located on both the main and upper levels.
Check the maps of those levels to see exactly where the Dewey books you're looking for are shelved. Eventually, all books will be classified by Library of Congress call numbers.