Charles Ellicott Commentary Romans 8:17

"and if children, then heirs; heirs of God, and joint-heirs with Christ; if so be that we suffer with [him], that we may be also glorified with [him]." — Romans 8:17 (ASV)

One characteristic of the son is that he is his father’s heir. So it is with the Christian. He, too, has an inheritance—an inheritance of glory which he will share with Christ. But he must not be surprised if, before sharing the glory, he also shares the sufferings.

Suffer with him.—All who suffer for the sake of the gospel are regarded as suffering with Christ. They drink of the cup that He drank of (Matthew 20:22–23). (Compare to 2 Corinthians 1:5; Philippians 3:10; Colossians 1:24).