​Hebrews 5:9

  • ​And being made perfect, he became the author of eternal salvation unto all them that obey him; (Hebrews 5:9)

We find in this another verse that is misconstrued to teach a false plan of salvation, where people are saying you have to keep the law (in so many words) to be saved.

However, in the context of salvation, one can obey Jesus Christ by believing the gospel:
  • And saying, The time is fulfilled, and the kingdom of God is at hand: repent ye, and believe the gospel. (Mark 1:15)

And believing the gospel is the same thing as obeying the gospel:
  • But they have not all obeyed the gospel. For Esaias saith, Lord, who hath believed our report? (Romans 10:16)
And the reference from Isaiah:
  • ¶ Who hath believed our report? and to whom is the arm of the LORD revealed? (Isaiah 53:1)
  • But he [was] wounded for our transgressions, [he was] bruised for our iniquities: the chastisement of our peace [was] upon him; and with his stripes we are healed. All we like sheep have gone astray; we have turned every one to his own way; and the LORD hath laid on him the iniquity of us all. (Isaiah 53:5-6)
We have to believe this gospel, found throughout the scriptures, old testament and new, to be saved.  

What are the consequences of not obeying the gospel?
  • For the time [is come] that judgment must begin at the house of God: and if [it] first [begin] at us, what shall the end [be] of them that obey not the gospel of God? (1 Peter 4:17)
  • 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; (2 Thessalonians 1:8-9)
They're the same as not believing the gospel:
  • In whom the god of this world hath blinded the minds of them which believe not, lest the light of the glorious gospel of Christ, who is the image of God, should shine unto them. (2 Corinthians 4:4)
  • ¶ For I am not ashamed of the gospel of Christ: for it is the power of God unto salvation to every one that believeth; to the Jew first, and also to the Greek. (Romans 1:16)
  • He that believeth on him is not condemned: but he that believeth not is condemned already, because he hath not believed in the name of the only begotten Son of God. (John 3:18)
  • I said therefore unto you, that ye shall die in your sins: for if ye believe not that I am [he], ye shall die in your sins. (John 8:24)

Finally, here's a new testament example of the gospel to be believed:
  • ¶ Moreover, brethren, I declare unto you the gospel which I preached unto you, which also ye have received, and wherein ye stand; By which also ye are saved, if ye keep in memory what I preached unto you, unless ye have believed in vain. For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures; And that he was buried, and that he rose again the third day according to the scriptures: (1 Corinthians 15:1-4)