This is the exchange as printed in the script (my emphasis added):
MOTTI: Any attack made by the Rebels against this station would be a useless gesture, no matter what technical data they've obtained. This station is now the ultimate power in the universe. I suggest we use it!
VADER: Don't be too proud of this technological terror you've constructed. The ability to destroy a planet is insignificant next to the power of the Force.
MOTTI: Don't try to frighten us with your sorcerer's ways, Lord Vader. Your sad devotion to that ancient religion has not helped you conjure up the stolen data tapes, or given you clairvoyance enough to find the Rebel's hidden fort...
Suddenly Motti chokes and starts to turn blue under Vader's spell.
VADER: I find your lack of faith disturbing.
Vader was disturbed by two things:
- Motti's lack of faith in the Force to help Vader fight the Rebels.
- Motti's undue faith in the Death Star over the Force.
Motti thought the Death Star cannot be destroyed (obviously Motti would shortly be proven wrong) and that it was the "ultimate power in the universe" instead of the Force (which is blasphemous to Vader, and also incorrect). As Vader indicated, the Force is still more powerful than the Death Star -- the Force cannot be destroyed and, while the Death Star can destroy a planet, the Empire owed its existence to the (dark side of the) Force.
Vader was disturbed by Motti's overconfidence in the Death Star at the expense of faith in the Force.