In cases where the history of the words was simple, such speculations have sometimes proved correct in the light of modern scholarship, but generally they were based on superficial similarities.
The purpose of etymology was to elucidate the spiritual background to a concept, drawing out aspects of semantics in a similar manner to the symbolic interpretation of the natural world.
An example: Hugh of Saint Victor derived the Latin word mors ('death') from morsus ('bite'): a morsu primi hominis qui vetitae arboris pomum mordens mortem incurrit ('from the bite of the first man, who, biting the apple of the forbidden tree, incurs death').
The fact that the same author knew other, alternative and logically incompatible etymologies for the same word (mors comes also from amarus, 'bitter', or from the name of the god of war Mars) did not devalue the lesson, since it was the spiritual meaning and not the philological accuracy which stood in the foreground.
As yet there is still no satisfactory history of Christian etymology, but a very useful discussion of it is that of Friedrich Ohly in his essay "On the spiritual sense of the word in the Middle Ages".