The first thing to note in Hebrews 10:26-27 is the word "sin." Paul is not speaking of sin in general but the specific sin of apostasy from the faith that was once known and professed. The apostasy he has in mind is not so much an act but a state brought on by many individual attitudes and sins, reproducing the original, carnal antagonism a person has toward God before conversion.
Some commentaries insist that the Authorized Version is not quite correct in translating the term in verse 26 as "willfully." These argue that the Greek word, hekousios, will not permit this translation. It appears only one other time, in I Peter 5:2, where it is translated as "willingly." The commentators insist that it should be rendered "willingly" in Hebrews 10:26.
The American Heritage College Dictionary supports their conclusion. To do something willfully is to do it purposely or deliberately. The commentators say all sin is done purposely because human nature is set up to do so, even though weakness, ignorance, or deception may be involved as well. To do a thing willingly is to be disposed, inclined, or prepared to do it. Its synonyms are "readily," "eagerly," "compliantly," "ungrudgingly," "voluntarily," and "volitionally." This sense is contained in the context because, by the time a person reaches the apostate stage in his backward slide, where he has forsaken God and His way, he has no resistance to sin.
The sinner is deliberately, even eagerly, determined to abandon Christ, to turn away from God and His way, having completely become an enemy once again. He sins with barely a second thought, if with any thought at all. He sins automatically, as there is none of God's Spirit left to constrain him. His conscience is totally defiled; he has forsaken God.
Who is in danger of committing this sin? All who have made a profession of faith in Christ but are now neglecting their salvation.
The message of Hebrews is that it does not have to be this way. If the person takes heed and stirs himself awake, if he truly seeks to overcome and grow once again, if he returns to being a living sacrifice and seeking to glorify God, if he truly denies himself and takes up his cross, if he keeps God's commandments to live life as a Christian, he will not apostatize.
He may fall back from time to time, but as long as he repents and honestly seeks God when sin occurs in his life, the sin is readily forgiven. I John 1:9 confidently proclaims, "If we confess our sins, He is faithful and just to forgive us our sins and to cleanse us from all unrighteousness." John 14:23 assures us that as long as we are keeping His Word, we are safe.
Hebrews 12:5-10 explains that God is faithfully working in our behalf, even chastening us if He sees fit, to get us turned around and headed again in the right direction and attitude. He does this faithfully because He does not want to lose us. Christ died for each child of God, thus each child He loves - and He loves them all - represents a substantial investment. Christ did not die in vain for anybody. In Hebrews 13:5, He charges us with the task of putting to work His promise, "I will never leave you nor forsake you."