9th letter = i
Only bible book beginning with "i" is Isaiah. "Isaiah" ends on a h. h is the 8th letter of the alphabet.
Isaiah 8:1 says
Young's Literal Translation
"And Jehovah saith unto me, 'Take to thee a great tablet, and write upon it with a graving tool of man, To haste spoil, enjoy prey.' "
So, Maher-shalal-hash-baz means "haste spoil, enjoy prey". That's a strange name to give to your child.