Which preposition to use with twofoldness

of Occurrences 1%

I confess that till the light of the twofoldness of the Christian Church dawned on my mind, the study of the history and literature of the Church during the first three or four centuries infected me with a spirit of doubt and disgust which required a frequent recurrence to the writings of John and Paul to preserve me whole in the Faith.

Which preposition to use with  twofoldness