"'The one who called you' (NIV), consistently with Paul's usage, denotes God (cf. v. 15); the Greek construction (article with participle) emphasizes the divine initiative (cf. 1 Thess. 2:12; 1 Pet. 1:15), while the particular tense used (aorist) suggests that God's call to the Galatians was mediated through the apostle's preaching of the gospel (cf. vv. 8f.)." (44)From the title of this post, you know I'm honing in on the aorist. I'm scratching my head trying to figure out how in the world Fung moves from the aorist tense to deducing that God's call was mediated by someone else. I'm at a loss. This is an example of how you have to be very careful when you're flipping through the commentaries or any publication for that matter. And this is where a basic, conceptual understanding of the Greek language will help someone as they work through study tools like commentaries, journal articles, and monographs.
There's a leap in this example from what the text says to what the author wants to say about the text. And when those leaps don't fall within what is permissible or possible within the grammar of a language, proposals such as the one above should be called into question. Students of the New Testament need to be as sharp at asking questions of the tools they use to study the New Testament as they are at asking questions of the New Testament text they are studying. Taking what a commentary says at face value, without a critical eye, is as dangerous to the study of the New Testament as studying the New Testament without asking any questions at all.
The tense of καλέσαντος says nothing about mediation. We know that God mediates his call through those who share the message of the cross with those who are dead in their trespasses and sins. We know that from numerous texts in the New Testament, especially Rom. 10:14c: "And how will they hear without a preacher?" But knowing that καλέσαντος is aorist communicates nothing about this mediation. What does the aorist tell us? Only that this act of calling took place sometime prior to the writing of Paul's letter. Paul's purpose on using the aorist is not so his audience can understand that God's messengers were the ones through whom that call was extended or realized. The focus is on identifying the one who the Galatians believers are thinking about turning away from. And he is the one who called the Galatians. We really shouldn't make more of the grammar than the grammar permits. Our task in explaining what the text means is just that––explaining what the text means.