1 Tim 1:2 wrote:Τιμοθέῳ γνησίῳ τέκνῳ ἐν πίστει·
decided to read through 1 Timothy, and came across this interesting little tidbit.
If we take πίστει as definite (nouns can be definite without the article if they are objects of prepositions.), ἐν makes it a dative of sphere, that is, "Timothy, genuine child in the faith." Then Paul here would be making a declaration that little Timmy is within the group of the elect. Now, if we take ἐν as an "instrumental" marker, we would have something like "Timothy, genuine child by faith. That is, seeing faith as the tool which made him a genuine child.
Which way would you go? Both of these seem like they could represent the grammar and context. Is there another nuance it could be?