In your struggle against sin, you have not yet resisted to the point of shedding your blood. (Hebrew 12:4)

The Greek word translated ‘struggle’ is ἀνταγωνίζομαι  antagónizomai, from anti ‘against’ and agónizomai ‘contend with’, whence English derives the verb ‘to agonise’.  The common usage of agónizomai was in the context of warfare or an athletic contest, and it refers to the physical, mental and emotional exertion in contending with an enemy.

The writer of Hebrews references Jesus in the garden of Gethsemane, who –

knelt down and prayed, saying, “Father, if you are willing, remove this cup from me. Nevertheless, not my will, but yours, be done.” And there appeared to him an angel from heaven, strengthening him. And being in an agony he prayed more earnestly; and his sweat became like great drops of blood falling down to the ground.And when he rose from prayer, he came to the disciples and found them sleeping for sorrow, and he said to them, “Why are you sleeping? Rise and pray that you may not enter into temptation.”  (Luke 22:42-46)

Jesus overcame the temptation to refuse the cup of suffering, but knew his disciples would also be tested and fail, exemplified by Peter’s thrice denial and the flight from Jerusalem.

It makes a mockery of the cross, if the one who professes faith believes that Jesus gives a free pass to sin.  He who exudes blood through fear of his ordeal yet resists sin, can rightfully demand nothing less from those who benefit from that suffering when they face temptation. 

His disciples are required to root out sin:

If your right eye causes you to sin, tear it out and throw it away. For it is better that you lose one of your members than that your whole body be thrown into hell. And if your right hand causes you to sin, cut it off and throw it away. For it is better that you lose one of your members than that your whole body go into hell. (Matthew 5:29-30)

While the figure of speech is hyperbole, in other words, deliberate exaggeration, such a metaphor evokes the extreme, radical and also emotionally painful process of eradicating sinful desire.

All are to search for the indwelling sinful nature – for if any think they are without sin, they are deluded and are not the body of Christ:

But if we walk in the light, as he is in the light, we have fellowship with one another, and the blood of Jesus his Son cleanses us from all sin. If we say we have no sin, we deceive ourselves, and the truth is not in us. If we confess our sins, he is faithful and just to forgive us our sins and to cleanse us from all unrighteousness. If we say we have not sinned, we make him a liar, and his word is not in us.  (1 John 1:7-10)

To deny residual sin is to deny the need for the cross.  Thus, are seen two deceptions common to humankind.

The first deception is that evil is without not within.  It is easy to see sin in others, and point to evil doers.  For this reason, Jesus forbids the judging of others, again employing metaphor:

Why do you see the speck that is in your brother’s eye, but do not notice the log that is in your own eye?(Matthew 7:3).

Indeed, when regarding others, the disciple of Christ may not condemn only forgive.  The personal pursuance of justice is sanctioned only to earthly authority and to Jesus himself, his followers are to be merciful.

While it is so much easier to see external evil, yet it is the only internal evil within we are licensed, and more critically, commanded to deal with.  Observance of this would have halted the persecution throughout history by the church in the name of Christ, which is rightly derided by the non-believer as hypocrisy and has brought calumny to the name Jesus.

The second deception is one far more insidious, one in which sin is self-defined.  Paul writes:

if it had not been for the law, I would not have known sin. (Romans 7:7a)

The law Paul is speaking about is of course the Mosaic Law, as the rest of the verse makes plain:

For I would not have known what it is to covet if the law had not said, “You shall not covet.” (ibid 7:7b – quoting Exodus 20:17, the tenth commandment).

Under the New Covenant the law is fulfilled as the Old Covenant made obsolete (Hebrews 8:13) but law not dispensed with.  Jesus restates nine of the ten commandments including ‘you shall not covet (your neighbour’s wife)’ and he extends the reach, into intention not just execution:

You have heard that it was said, ‘You shall not commit adultery.’  But I tell you that anyone who looks at a woman lustfully has already committed adultery with her in his heart. (Matthew 5:27-28)

To follow Jesus is then to live according to his commandments in thought and deed; and everywhere in the Gospels and the letters of the Apostles obeying his commandments is the basis of the relationship with him:

If you keep my commands, you will remain in my love…you are my friends if you do what I command. (John 15:10a & 14)

Jesus reiterated the Word of God and he expected it be observed:

Blessed rather are those who hear the word of God and obey it.  (Luke 11:28)

And it is obedience evidences the validity of the relationship:

We know that we have come to know him if we keep his commands. Whoever says, ‘I know him,’ but does not do what he commands is a liar, and the truth is not in that person. (1 John 2:3-4)

Therefore, God defines the terms of this relationship and Jesus makes it clear in his teachings.  To disobey is to sin, thus the only fixed definition of sin is provided by the Bible, and specifically in the commandments of Jesus.  

Putting aside Jesus’ commandments in favour of one’s own means putting oneself as the arbiter of law, in other words being the judge of morality, purity and holiness.  To this the answer is:

There is only one lawgiver and judge, he who is able to save and to destroy. But who are you to judge your neighbour?  (James 4:12)

Or extending James’ words: who are you to judge yourself?  The deception that conscious alone, or even the prevailing morality of one’s culture provides the benchmark of what is sinful, is all pervading.  The only true guidance of what God wills to be right and just are the commandments of Jesus.

To understand Jesus’ work is thus the foundation for that of his followers is to grasp the difference between justification and sanctification.  One is the sovereign work of God, the other is extent to which one cooperates actively with the Holy Spirit, and both affect the quality of one’s eternity.

Sanctification is a process of alignment with Godly morality, through choices to adhere to the framework of His Word through the iteration of Jesus’ commandments, but God does not do this without promise of reward; facing his imminent execution from his prison cell in Rome, Paul reflects to Timothy:

 I have fought the good fight, I have finished the race, I have kept the faith.  Now there is in store for me the crown of righteousness, which the Lord, the righteous Judge, will award to me on that day… (2 Timothy 4:7-8)

The Day of Judgement also brings reward but also loss for the believer.  Referring to each person’s choices to live their life in God’s ways in adherence or repudiation in terms of occupation:

…the Day will bring (the work) to light. It will be revealed with fire, and the fire will test the quality of each person’s work. If what has been built survives, the builder will receive a reward. If it is burned up, the builder will suffer loss but yet will be saved—even though only as one escaping through the flames.  (1 Corinthians 3:13-14)

Loss then is not the loss of salvation, but it is loss nonetheless.  Loss that will be keenly felt in eternity as if being scorched by fire.

It is seen then, that salvation is confirmed as the gift of God by the salvatory work of the Cross of Christ.  This is a unilateral act.  The step of faith that all must take, is seen in retrospect as irresistible grace.  And that must be because none oblige God to accept and redeem them.  

But once redeemed, or justified and made righteous through the atoning sacrifice, there begins the work of the justified, and without this work there can be no assurance of salvation. 

It comes down to faith in the end, of course.  If any truly believe that Jesus bore the God’s wrath on their behalf for every sin they committed, why would any add to this punishment by sinning further?  It is not simply out of gratitude but to minimise his suffering, that all must deny their will and do God’s. And this how Jesus knows we love him:

If you love me, you will keep my commandments. (John 14:15)

If any continue to sin, in what is their faith?  Is it even the faith that ensures salvation, if the Jesus that is the subject of that profession is not obeyed?

It is the final commandment of Jesus that the follower brings him or herself under discipline and teach others to do so:

Therefore, go and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, and teaching them to obey everything I have commanded you.  And surely, I am with you always, to the very end of the age.

(Matthew 28:19-20)

If baptism signifies spiritual rebirth of justification, the walk of obedience is sanctification, and both are necessary for the assurance of Jesus’ presence.