I read this on the Chaldean numerology site...

As you may already have noticed, no alphabet letter was assigned to the number 9. The reason why the number 9 was omitted under Chaldean Numerology system was because the Chaldeans felt the 9 was holy, sacred, and thus to be held apart from the rest. However, should your name or that of someone you know total 9, then the 9 remains. Let's analyze a sample name under Chaldean Numerology system:

I was under the impression that the reason that the Chaldean's did not use the number 9 was because man had not yet reached that stage in his evolution of the brotherhood, of his oneness. 

"What lies behind us and what lies before us are small matters compared to what lies within us."  ~ Ralph Waldo Emerson ~