Once saved always saved?

John 3:16

For God so loved the world that He gave His one and only Son, that whoever believes in Him shall not perish but have eternal life.

Romans 10:9

... if you confess with your mouth, “Jesus is Lord,” and believe in your heart that God raised Him from the dead, you will be saved.

Romans 8:1

Therefore, there is now no condemnation for those who are in Christ Jesus ...

Romans 6:14

... you are not under Law, but under grace.

Galatians 2:16

... a man is not justified by observing the Law, but by faith in Jesus Christ. So we, too, have put our faith in Christ Jesus that we may be justified by faith in Christ and not by observing the Law, because by observing the Law no one will be justified.

Colossians 1:22-23

... He has reconciled you by Christ’s physical body through death to present you holy in His sight, without blemish and free from accusation – if you continue in your faith, established and firm, not moved from the hope held out in the gospel.

1 Corinthians 15:1-4

“Now, brothers, I want to remind you of the gospel I preached to you, which you received and on which you have taken your stand. By this gospel you are saved, if you hold firmly to the word I preached to you. Otherwise, you have believed in vain.

“For what I received I passed on to you as of first importance: that Christ died for our sins according to the Scriptures, that He was buried, that He was raised on the third day according to the Scriptures ...”

Ephesians 2:8-9

“For it is by grace you have been saved, through faith – and this not from yourselves, it is the gift of God – not by works, so that no one can boast.”

Hebrews 2:1-3

“We must pay more careful attention, therefore, to what we have heard, so that we do not drift away. For if the message spoken by angels was binding, and every violation and disobedience received its just punishment, how shall we escape if we ignore such a great salvation?”

Hebrews 3:7-19

So, as the Holy Spirit says:
“Today, if you hear His voice, do not harden your hearts as you did in the rebellion, during the time of testing in the desert, where your fathers tested and tried Me and for forty years saw what I did.
That is why I was angry with that generation, and I said, ‘Their hearts are always going astray, and they have not known My ways.’
So I declared on oath in My anger, ‘They shall never enter My rest.’”

See to it, brothers, that none of you has a sinful, unbelieving heart that turns away from the living God. But encourage one another daily, as long as it is called Today, so that none of you may be hardened by sin’s deceitfulness. We have come to share in Christ if we hold firmly till the end the confidence we had at first. As has just been said:
“Today, if you hear His voice, do not harden your hearts as you did in the rebellion.”

Who were they who heard and rebelled? Were they not all those Moses led out of Egypt? And with whom was He angry for forty years? Was it not with those who sinned, whose bodies fell in the desert? And to whom did God swear that they would never enter His rest if not to those who disobeyed? So we see that they were not able to enter, because of their unbelief.

Hebrews 6:4-12

It is impossible for those who have once been enlightened, who have tasted the heavenly gift, who have shared in the Holy Spirit, who have tasted the goodness of the word of God and the powers of the coming age, if they fall away, to be brought back to repentance, because to their loss they are crucifying the Son of God all over again and subjecting Him to public disgrace.

Land that drinks in the rain often falling on it and that produces a crop useful to those for whom it is farmed receives the blessing of God. But land that produces thorns and thistles is worthless and is in danger of being cursed. In the end it will be burned.

Even though we speak like this, dear friends, we are confident of better things in your case – things that accompany salvation. God is not unjust; He will not forget your work and the love you have shown Him as you have helped His people and continue to help them. We want each of you to show this same diligence to the very end, in order to make your hope sure. We do not want you to become lazy, but to imitate those who through faith and patience inherit what has been promised.

Hebrews 10:26-31

If we deliberately keep on sinning after we have received the knowledge of the truth, no sacrifice for sins is left, but only a fearful expectation of judgment and of raging fire that will consume the enemies of God. Anyone who rejected the law of Moses died without mercy on the testimony of two or three witnesses. How much more severely do you think a man deserves to be punished who has trampled the Son of God under foot, who has treated as an unholy thing the blood of the covenant that sanctified him, and who has insulted the Spirit of grace? For we know Him who said, “It is mine to avenge; I will repay,” and again, “The Lord will judge His people.” It is a dreadful thing to fall into the hands of the living God.

Hebrews 12:14-17,25

Make every effort to live in peace with all men and to be holy; without holiness no one will see the Lord. See to it that no one misses the grace of God and that no bitter root grows up to cause trouble and defile many. See that no one is sexually immoral, or is godless like Esau, who for a single meal sold his inheritance rights as the oldest son. Afterward, as you know, when he wanted to inherit this blessing, he was rejected. He could bring about no change of mind, though he sought the blessing with tears.

See to it that you do not refuse Him who speaks. If they did not escape when they refused Him who warned them on earth, how much less will we, if we turn away from Him who warns us from heaven?

John 14:15-19

“If you love Me, you will obey what I command. And I will ask the Father, and He will give you another Counselor to be with you forever – the Spirit of truth. The world cannot accept Him, because it neither sees Him nor knows Him. But you know Him, for He lives with you and will be in you. I will not leave you as orphans; I will come to you. Before long, the world will not see Me anymore, but you will see Me. Because I live, you also will live.”

2 Corinthians 4:7

But we have this treasure in jars of clay to show that this all-surpassing power is from God and not from us.

Romans 8:11

... if the Spirit of Him who raised Jesus from the dead is living in you, He who raised Christ from the dead will also give life to your mortal bodies through His Spirit, who lives in you.

Hebrews 12:1-8

Therefore, since we are surrounded by such a great cloud of witnesses, let us throw off everything that hinders and the sin that so easily entangles, and let us run with perseverance the race marked out for us. Let us fix our eyes on Jesus, the author and perfecter of our faith, who for the joy set before Him endured the cross, scorning its shame, and sat down at the right hand of the throne of God. Consider Him who endured such opposition from sinful men, so that you will not grow weary and lose heart.

In your struggle against sin, you have not yet resisted to the point of shedding your blood. And you have forgotten that word of encouragement that addresses you as sons:
“My son, do not make light of the Lord’s discipline, and do not lose heart when He rebukes you, because the Lord disciplines those He loves, and He punishes everyone He accepts as a son.”

Endure hardship as discipline; God is treating you as sons. For what son is not disciplined by his father? If you are not disciplined (and everyone undergoes discipline), then you are illegitimate children and not true sons.

2 Timothy 4:7-8

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 – and not only to me, but also to all who have longed for His appearing.

2 Corinthians 12:9-10

But He said to me, “My grace is sufficient for you, for My power is made perfect in weakness.” Therefore I will boast all the more gladly about my weaknesses, so that Christ’s power may rest on me. That is why, for Christ’s sake, I delight in weaknesses, in insults, in hardships, in persecutions, in difficulties. For when I am weak, then I am strong.