I am having trouble understanding this sentence from Living Latin: A Graded Reader:
Pro isto vestro in me officio pares agere gratias vix possum, referre nequaquam!
I guess it means something like
I can hardly thank you enough for this favor you have done for me, let alone repay it!
But I can't parse the grammar of the first part of the sentence, "in me officio" is "for me", but "pares" and "vestro" sound out of place to me. I am surprised there is no relative clause.
You have the general idea, but in me officio doesn't go together to mean 'for me.'
Pares modifies the accusative gratias, and the phrase means 'equal thanks.'
Vestro, like isto, modifies the ablative officio, which is the object of the preposition pro. Therefore the phrase means 'for that service/favor of yours.'
The prepositional phrase in me (where me is accusative) limits officio, 'duty toward me.'
Therefore, the first part of the sentence means, 'I am scarcely able to give equal thanks for that service/favor of yours toward me.' A relative clause could have been used to express 'that service/favor that you did for me,' but the prepositional phrase (in me) gets the idea across just as well and without cluttering the sentence.
