Hebrews 10:26-31

26 For if we go on sinning deliberately after receiving the knowledge of the truth, there no longer remains a sacrifice for sins, 27 but a fearful expectation of judgment, and a fury of fire that will consume the adversaries. 28 Anyone who has set aside the law of Moses dies without mercy on the evidence of two or three witnesses. 29 How much worse punishment, do you think, will be deserved by the one who has trampled underfoot the Son of God, and has profaned the blood of the covenant by which he was sanctified, and has outraged the Spirit of grace? 30 For we know him who said, “Vengeance is mine; I will repay.” And again, “The Lord will judge his people.” 31 It is a fearful thing to fall into the hands of the living God.
Hebrews 10:26-31 (ESV)


Hebrews 6:1-12

Therefore let us leave the elementary doctrine of Christ and go on to maturity, not laying again a foundation of repentance from dead works and of faith toward God, and of instruction about washings, the laying on of hands, the resurrection of the dead, and eternal judgment. And this we will do if God permits. For it is impossible, in the case of those who have once been enlightened, who have tasted the heavenly gift, and have shared in the Holy Spirit, and have tasted the goodness of the word of God and the powers of the age to come, and then have fallen away, to restore them again to repentance, since they are crucifying once again the Son of God to their own harm and holding him up to contempt. For land that has drunk the rain that often falls on it, and produces a crop useful to those for whose sake it is cultivated, receives a blessing from God. But if it bears thorns and thistles, it is worthless and near to being cursed, and its end is to be burned.
Though we speak in this way, yet in your case, beloved, we feel sure of better things—things that belong to salvation. 10 For God is not unjust so as to overlook your work and the love that you have shown for his name in serving the saints, as you still do. 11 And we desire each one of you to show the same earnestness to have the full assurance of hope until the end, 12 so that you may not be sluggish, but imitators of those who through faith and patience inherit the promises.
Hebrews 6:1-12 (ESV)

Hebrews 4:1-11

Therefore, while the promise of entering his rest still stands, let us fear lest any of you should seem to have failed to reach it. For good news came to us just as to them, but the message they heard did not benefit them, because they were not united by faith with those who listened. For we who have believed enter that rest, as he has said,
“As I swore in my wrath,
‘They shall not enter my rest,'”
although his works were finished from the foundation of the world. For he has somewhere spoken of the seventh day in this way: “And God rested on the seventh day from all his works.” And again in this passage he said,
“They shall not enter my rest.”
Since therefore it remains for some to enter it, and those who formerly received the good news failed to enter because of disobedience, again he appoints a certain day, “Today,” saying through David so long afterward, in the words already quoted,
“Today, if you hear his voice,
do not harden your hearts.”
For if Joshua had given them rest, God would not have spoken of another day later on. So then, there remains a Sabbath rest for the people of God, 10 for whoever has entered God’s rest has also rested from his works as God did from his.
11 Let us therefore strive to enter that rest, so that no one may fall by the same sort of disobedience. 
Hebrews 4:1-11 (ESV)

Hebrews 3:6-19

 but Christ is faithful over God’s house as a son. And we are his house, if indeed we hold fast our confidence and our boasting in our hope.

Therefore, as the Holy Spirit says,

“Today, if you hear his voice,
8 do not harden your hearts as in the rebellion,
on the day of testing in the wilderness,
9 where your fathers put me to the test
and saw my works for forty years.
10 Therefore I was provoked with that generation,
and said, ‘They always go astray in their heart;
they have not known my ways.’
11 As I swore in my wrath,
‘They shall not enter my rest.'”
12 Take care, brothers, lest there be in any of you an evil, unbelieving heart, leading you to fall away from the living God. 13 But exhort one another every day, as long as it is called “today,” that none of you may be hardened by the deceitfulness of sin. 14 For we have come to share in Christ, if indeed we hold our original confidence firm to the end. 15 As it is said,
“Today, if you hear his voice,
do not harden your hearts as in the rebellion.”
16 For who were those who heard and yet rebelled? Was it not all those who left Egypt led by Moses? 17 And with whom was he provoked for forty years? Was it not with those who sinned, whose bodies fell in the wilderness? 18 And to whom did he swear that they would not enter his rest, but to those who were disobedient? 19 So we see that they were unable to enter because of unbelief.
Hebrews 3:6-19 (ESV)

Hebrews 2:1-3

Therefore we must pay much closer attention to what we have heard, lest we drift away from it. For since the message declared by angels proved to be reliable, and every transgression or disobedience received a just retribution, how shall we escape if we neglect such a great salvation? It was declared at first by the Lord, and it was attested to us by those who heard,
Hebrews 2:1-3 (ESV)


Titus 1:15-16

To the pure, all things are pure, but to the defiled and unbelieving, nothing is pure; but both their minds and their consciences are defiled. 16 They profess to know God, but they deny him by their works. They are detestable, disobedient, unfit for any good work.
Titus 1:15-16 (ESV)