“For I am not ashamed of the gospel, for it is the power of God for salvation to everyone who believes, to the Jew first and also to the Greek” (Romans 1.16).
Both Paul (Romans 10.16) and Peter (1 Peter 4.17) use the expression “obey the gospel.” The primary idea in obedience is submission. We must submit to Christ as sin-offering to be saved by Him. Obedience to Christ as teacher and king is not enough. We must obey, submit, to Him as sin-offering.
But how can we “obey the gospel” unless in our obedience we are responding to Christ as sin-offering? How can we “obey the gospel” unless our obedience relates directly to the gospel? Why didn’t Paul and Peter simply demand obedience to Christ as one in authority? Because they understood that Christ saves by means of His death on our behalf, not simply by His authority, but by His propitiation.
When, therefore, does belief, repentance, and baptism constitute “obeying the gospel”? The gospel is the death, burial, and resurrection of Christ (1 Corinthians 15.3-4). The conditions of belief, repentance, and baptism constitute “obeying the gospel” only when they are responses to and express reliance upon the crucified Christ. To obey in those respects simply because we have been commanded to is to ignore the cross and render it void.
Faith in Christ is faith or trust in Him as the sacrifice for our sins. Merely believing in Him as God’s Son with no thought of the cross is not enough. Likewise, repentance with no thought of His crucifixion or baptism except as a response to His death for our sins, are not enough.
“Do you not know that all of us who have been baptized into Christ Jesus were baptized into his death? We were buried therefore with him by baptism into death, in order that, just as Christ was raised from the dead by the glory of the Father, we too might walk in newness of life” (Romans 6.3-4).
In “obeying the gospel” we should know that we are responding to the blood of Christ and not merely recognizing the right of Christ to demand our obedience.