Joint-heirs with Christ (sunklhronomoi Cristou). A late rare double compound, in Philo, an Ephesian inscription of the imperial period (Deissmann, Light from the Ancient East, p. 92), papyri of the Byzantine period. See 1 John 8:29 for this idea expanded. Paul is fond of compounds of sun, three in this verse (sunklhronomoi, sunpascwmen, sundoxasqwmen). The last (first aorist passive subjunctive of sundoxazw with ina (purpose), late and rare, here only in N.T.