Hebrews 5:9 states:
“And being made perfect, he became the author of eternal salvation unto all them that obey him.”
At first glance, this passage raises an important question: in what sense must one “obey” Christ to receive eternal salvation?
With respect to eternal salvation, obedience to Christ is indeed required—but not in the sense of maintaining a subjective standard of moral performance, as is so often assumed. Rather, Scripture consistently teaches that the obedience required for salvation is obedience to the gospel itself. Those who hear the gospel obey Christ by believing the gospel.
Paul makes this explicit in Romans 10:16:
“But they have not all obeyed the gospel. For Esaias saith, Lord, who hath believed our report?”
Notice the parallelism. To disobey the gospel is to refuse to believe it. Conversely, the gospel is obeyed when it is believed.
The same contrast appears in 2 Thessalonians 1:8–10:
“In flaming fire taking vengeance on them that know not God, and that obey not the gospel of our Lord Jesus Christ:
Who shall be punished with everlasting destruction from the presence of the Lord, and from the glory of his power;
When he shall come to be glorified in his saints, and to be admired in all them that believe (because our testimony among you was believed) in that day.”
Here, Paul contrasts those “that obey not the gospel” (v. 8) with those who believe (v. 10), once again demonstrating that obedience to the gospel is synonymous with believing the gospel.
That said, once an individual believes in Christ and becomes a child of God, there is another sense in which obedience is necessary—one that does not contradict either the free grace of God or the free will of man.
Consider an earthly illustration. My children are expected to obey their father; obedience in my household is not optional. Though my children possess free will and may choose to disobey, they do not do so without consequence. Yet their status as my children is not conditioned upon their obedience.
In the same way, while my sonship before God is not conditioned upon my obedience, I am nonetheless called to obey my Father in heaven. For this reason, the charge that “free grace” makes obedience optional fails to stand once proper biblical distinctions are made.
Hebrews 12:5–6 affirms this truth:
“And ye have forgotten the exhortation which speaketh unto you as unto children, My son, despise not thou the chastening of the Lord, nor faint when thou art rebuked of him: For whom the Lord loveth he chasteneth, and scourgeth every son whom he receiveth.”
In conclusion,
Individuals must obey the gospel to be saved—that is, they must believe in Christ. Once saved, the child of God is called to obey his heavenly Father, not to remain saved or to prove the legitimacy of his sonship, but because of the relationship that now exists. Just as my children are expected to obey me and are corrected when they do not, so also the children of God are expected to obey their Father in heaven. In this sense, obedience is necessary for the child of God.