A.T. Robertson Commentary Ephesians 3:6

"[to wit], that the Gentiles are fellow-heirs, and fellow-members of the body, and fellow-partakers of the promise in Christ Jesus through the gospel," — Ephesians 3:6 (ASV)

To wit . Not in the Greek. But the infinitive (εινα) clause is epexegetical and gives the content of the revelation, a common idiom in the N.T. Τα εθνη is in the accusative of general reference. Paul is fond of compounds with συν and here uses three of them.

Fellow-heirs (συνκληρονομα). Late and rare (Philo, inscriptions and papyri). See also Ro 8:17.

Fellow-members of the body (συνσωμα). First found here and only here save in later ecclesiastical writers. Preuschen argues that it is equivalent to συνδουλος in Col 1:7 (σωμα in sense of δουλος).

Fellow-partakers (συνμετοχα). Another late and rare word (Josephus). Only here in N.T. In one papyrus in sense of joint possessor of a house.