I have always loved the details of exegesis, which in my mind should often be described as the pursuit to explain everything, that is, exegesis properly explains everything we see in a text, from major affirmations down to single words. I came across a good example of this in Galatians 1:16. Here's the verse along with the prior one for context. The phrase I'm interested in is in bold:
But when the one who set me apart from birth and called me by his grace was pleased to reveal his Son in me so that I could preach him among the Gentiles, I did not go to ask advice from any human being
The question I'm pondering here is, should ἀποκαλύψαι τὸν υἱὸν αὐτοῦ ἐν ἐμοί be translated as "to reveal his Son in me" or "to me"? In other words, what is the meaning of the preposition ἐν here? The difference in translation is slight, but the difference in meaning is rather profound. One the one hand Paul could simply identify himself as the recipient of this revelation; he then in turn conveys that revelation to others. But if Paul here indicates the location of the revelation, that is, in Paul himself Christ is revealed, then Paul identifies himself as the conduit or passageway for the revelation which is then passed on to others. The latter meaning has more theological significance because it places great stress upon Paul's life and activity as an apostle as the means by which Christ is revealed to the world: In Paul's very person Christ is revealed and then shown to others. Both meanings are possible for this preposition, as the NET Bible note here indicates. The use of the verb ἀποκαλύψαι could naturally imply "to me" in that it would show to whom the revelation was given (for this see BDAG s.v. ἀποκαλύπτω, section c). This verb begs for a recipient to be identified in the context. This occurs often enough in the NT with this verb and the simple dative (Matt 11:25; 16:17; Luke 10:21; 1 Cor 14:30; Eph 3:5; 1 Pet 1:12). But here in Galatians 1:16 the preposition ἐν occurs as well. Even though it is theoretically possible that the preposition ἐν can function like the simple dative and thus could indicate the indirect object here, Paul's usage of the simple dative and this verb elsewhere would indicate that inclusion of the preposition was meaningful. In addition, in his argument in v. 15-16 Paul speaks of a deeper attachment to the purposes of God than simply being a mouthpiece; rather he was chosen as a special instrument of God. The better conclusion is that ἐν ἐμοί indicates that Paul is the locus of the revelation, and as such "in me" is the appropriate translation. Paul is thus arguing that the revelation of Jesus Christ was not just "to him" on the Damascus road but "in him" through his preaching, ministry, and life.
This is similar to the argument Lightfoot makes about this phrase in his commentary (p. 83 in the 10th edition):
It does not speak of a revelation made inwardly to himself, but of a revelation made through him to others. The preposition ἐν is used in preference to διά, because St Paul was not only the instrument in preaching the Gospel, but also in his own person bore the strongest testimony to its power.