There are several things going on in James 3:6. Two of the more interesting are the placement of γλῶσσα and whether καθίσταται is a middle or passive.

“And the tongue is a fire (ἡ γλῶσσα πῦρ)! The tongue is a world of iniquity (ὁ κόσμος τῆς ἀδικίας ἡ γλῶσσα) set among our members (καθίσταται ἐν τοῖς μέλεσιν ἡμῶν ); it defiles the whole body (ἡ σπιλοῦσα ὅλον τὸ σῶμα), sets on fire the course of our life (καὶ φλογίζουσα τὸν τροχὸν τῆς γενέσεως), and is set on fire by hell (καὶ φλογιζομένη ὑπὸ τῆς γεέννης).”

If the second γλῶσσα goes with the preceding, it means “The tongue is a (or “the”) world of iniquity, and this means that the subject of καθίσταται is drawn from its personal ending.

If γλῶσσα goes with the following, then κόσμος τῆς ἀδικίας is a noun phrase in apposition to γλῶσσα (“The tongue is a fire, a world of iniquity”) and the second γλῶσσα is the subject of καθίσταται. “And the tongue is a fire. The tongue, a world of unrighteousness, is placed among our members” (CSB).

I will phrase this verse in a video to lay out it’s structure.

But the more significant challenge is the voice of καθίσταται.

In Peter’s sermon on the eschatological outpouring of the Holy Spirit, he says this. “The promise is for you and your children and for all who are far off—for all whom the Lord our God will call (προσκαλέσηται)” (NIV).

There are two problems with this translation. (1) It does not particularly make sense. Call what? (2) Why is προσκαλέσηται middle?

The point, of course, is to point out the scope of God’s salvation. Joel has already said that “everyone who calls on the name of the Lord will be saved” (Acts 2:21); that is the human side of salvation. Now, in v 39, is the divine side of God calling people.

And to be fair to the NIV, their English is reflecting the Hebrew (ארק; qal) and the LXX (προσκέκληται; perfect, not Luke’s aorist).