“The Spirit himself bears witness with our spirit that we are children of God, and if children, then heirs—heirs of God and fellow heirs with Christ, provided we suffer with him in order that we may also be glorified with him.” – Romans 8:16-17 (ESV)
“[T]his glorious inheritance is attained only through suffering. Because we are one with Christ, we are his fellow heirs, assured of being “glorified with him.” But, at the same time, this oneness means that we must follow Christ’s own road to glory, “suffering with him” (cf. also Phil. 1:29; 3:10; 2 Cor. 1:5)… [T]he suffering Paul speaks of here refers to the daily anxieties, tensions, and persecutions that are the lot of those who follow the one who was “reckoned with the transgressors” (Luke 22:37). Paul makes clear that this suffering is the condition for the inheritance; we will be “glorified with” Christ (only) if we “suffer with him.” Participation in Christ’s glory can come only through participation in his suffering… the glory of the kingdom of God is attained only through participation in Christ, and belonging to Christ cannot but bring our participation in the sufferings of Christ. Just as, then, Christ has suffered and entered into his glory (1 Pet. 1:11), so Christians, “fellow heirs with Christ,” suffer during this present time in order to join Christ in glory.”
– Douglas Moo, Romans (Grand Rapids: Eerdmans, 1996), 505-506.
“Suffering is the path to future glorification.”
– Thomas Schreiner, Romans (Grand Rapids: Baker, 1998), 428