In the Scriptures, there have been some who once served God but then later on left Him. Jude 1:5-6;11-13 I will therefore put you in remembrance, though ye once knew this, how that the Lord, having saved the people out of the land of Egypt, afterward destroyed them that believed not. And the angels which kept not their first estate, but left their own habitation, he hath reserved in everlasting chains under darkness unto the judgment of the great day. Woe unto them! for they have gone in the way of Cain, and ran greedily after the error of Balaam for reward, and perished in the gainsaying of Core. These are spots in your feasts of charity, when they feast with you, feeding themselves without fear: clouds they are without water, carried about of winds; trees whose fruit withereth, without fruit, twice dead, plucked up by the roots; Raging waves of the sea, foaming out their own shame; wandering stars, to whom is reserved the blackness of darkness for ever. Proverbs 21:16 The man that wandereth out of the way of understanding shall remain in the congregation of the dead. 2 Peter 2:22 But it is happened to them according to the true proverb, The dog is turned to his own vomit again; and the sow that was washed to her wallowing in the mire. The teaching or doctrine of eternal security is based upon the words of Bishop Augustine (354-430). He was a Roman Catholic who greatly impacted the world of theology, and taught the impossibility of falling away or apostasy (Eternal Security). As well as the supreme authority of the Roman church, and that mankind has no free will. Also purgatory, prayers for the dead, and that sex is sinful because depravity is inherited.
God's promises have always have been conditional. 2 Chronicles 7:12-22 And the LORD appeared to Solomon by night, and said unto him, I have heard thy prayer, and have chosen this place to myself for an house of sacrifice. If I shut up heaven that there be no rain, or if I command the locusts to devour the land, or if I send pestilence among my people; If my people, which are called by my name, shall humble themselves, and pray, and seek my face, and turn from their wicked ways; then will I hear from heaven, and will forgive their sin, and will heal their land. Now mine eyes shall be open, and mine ears attent unto the prayer that is made in this place. For now have I chosen and sanctified this house, that my name may be there for ever: and mine eyes and mine heart shall be there perpetually. And as for thee, if thou wilt walk before me, as David thy father walked, and do according to all that I have commanded thee, and shalt observe my statutes and my judgments; Then will I stablish the throne of thy kingdom, according as I have covenanted with David thy father, saying, There shall not fail thee a man to be ruler in Israel. But if ye turn away, and forsake my statutes and my commandments, which I have set before you, and shall go and serve other gods, and worship them; Then will I pluck them up by the roots out of my land which I have given them; and this house, which I have sanctified for my name, will I cast out of my sight, and will make it to be a proverb and a byword among all nations. And this house, which is high, shall be an astonishment to every one that passeth by it; so that he shall say, Why hath the LORD done thus unto this land, and unto this house? And it shall be answered, Because they forsook the LORD God of their fathers, which brought them forth out of the land of Egypt, and laid hold on other gods, and worshipped them, and served them: therefore hath he brought all this evil upon them.
Christians are advised to be afraid of God because as God cut off the natural olive branches from the olive tree (Israel), God will also cut them off if they get into unbelief. Romans 11:17-24 And if some of the branches be broken off, and thou, being a wild olive tree, wert graffed in among them, and with them partakest of the root and fatness of the olive tree; Boast not against the branches. But if thou boast, thou bearest not the root, but the root thee. Thou wilt say then, The branches were broken off, that I might be graffed in. Well; because of unbelief they were broken off, and thou standest by faith. Be not highminded, but fear: For if God spared not the natural branches, take heed lest he also spare not thee. Behold therefore the goodness and severity of God: on them which fell, severity; but toward thee, goodness, if thou continue in his goodness: otherwise thou also shalt be cut off. And they also, if they abide not still in unbelief, shall be graffed in: for God is able to graff them in again. For if thou wert cut out of the olive tree which is wild by nature, and wert graffed contrary to nature into a good olive tree: how much more shall these, which be the natural branches, be graffed into their own olive tree? If that happens, then spiritual life would cease to exist the same as life ceases to exist for a branch if it is cut off from the tree.
Jesus himself also taught against eternal security. In Matthew 25:26-30, Jesus himself taught the parable of the talents to show forth that point. This is what he said about the servant who was given one talent and did nothing with it. He said: "His lord answered and said unto him, Thou wicked and slothful servant, thou knewest that I reap where I sowed not, and gather where I have not strawed: Thou oughtest therefore to have put my money to the exchangers, and then at my coming I should have received mine own with usury. Take therefore the talent from him, and give it unto him which hath ten talents. For unto every one that hath shall be given, and he shall have abundance: but from him that hath not shall be taken away even that which he hath. And cast ye the unprofitable servant into outer darkness: there shall be weeping and gnashing of teeth." The talent was taken from him and given to the one who had the ten talents. And that worthless servant was thrown outside, into the darkness, where there was weeping and gnashing of teeth. That place is the fiery furnace (Matthew 13:41-42). "The Son of man shall send forth his angels, and they shall gather out of his kingdom all things that offend, and them which do iniquity; And shall cast them into a furnace of fire: there shall be wailing and gnashing of teeth."
Revelations 22:18-19 For I testify unto every man that heareth the words of the prophecy of this book, If any man shall add unto these things, God shall add unto him the plagues that are written in this book: And if any man shall take away from the words of the book of this prophecy, God shall take away his part out of the book of life, and out of the holy city, and from the things which are written in this book. In Revelations 22:18-19 we read what John wrote about God’s actions. The Lord’s apostles taught God would take away anyone’s share in the tree of life and the holy city, if they sinned in that manner. That’s the God of the Bible. John 15:1-6 I am the true vine, and my Father is the husbandman. Every branch in me that beareth not fruit he taketh away: and every branch that beareth fruit, he purgeth it, that it may bring forth more fruit. Now ye are clean through the word which I have spoken unto you. Abide in me, and I in you. As the branch cannot bear fruit of itself, except it abide in the vine; no more can ye, except ye abide in me. I am the vine, ye are the branches: He that abideth in me, and I in him, the same bringeth forth much fruit: for without me ye can do nothing. If a man abide not in me, he is cast forth as a branch, and is withered; and men gather them, and cast them into the fire, and they are burned. Jesus taught that God the father will cut off every branch from the vine that bears no fruit. Such branches will then wither or die and get thrown into the fire. God will send people to hell who were previously in Christ but were not fruitful.
Jesus said God can destroy our soul in hell, which would be impossible if the eternal security or once saved, always saved was true. Matthew 10:28 And fear not them which kill the body, but are not able to kill the soul: but rather fear him which is able to destroy both soul and body in hell. Luke 12:4-5 And I say unto you my friends, Be not afraid of them that kill the body, and after that have no more that they can do. But I will forewarn you whom ye shall fear: Fear him, which after he hath killed hath power to cast into hell; yea, I say unto you, Fear him. Jesus was talking to His disciples when He said the follow words. John 15:14 Ye are my friends, if ye do whatsoever I command you.That warning was given directly to those who had been saved. We are to fear God because he can send our souls into hell because of disobedience. This type of God is not compatible with the doctrine of eternal security.
Romans 8:31-39 is often used in defense of the eternal security doctrine. "What shall we then say to these things? If God be for us, who can be against us? He that spared not his own Son, but delivered him up for us all, how shall he not with him also freely give us all things? Who shall lay any thing to the charge of God's elect? It is God that justifieth. Who is he that condemneth? It is Christ that died, yea rather, that is risen again, who is even at the right hand of God, who also maketh intercession for us. Who shall separate us from the love of Christ? shall tribulation, or distress, or persecution, or famine, or nakedness, or peril, or sword? As it is written, For thy sake we are killed all the day long; we are accounted as sheep for the slaughter. Nay, in all these things we are more than conquerors through him that loved us. For I am persuaded, that neither death, nor life, nor angels, nor principalities, nor powers, nor things present, nor things to come, Nor height, nor depth, nor any other creature, shall be able to separate us from the love of God, which is in Christ Jesus our Lord." The one thing not mentioned that can separate us from God is ourselves. God will never force anyone to serve Him, unlike Satan who demands and forces people to devote themselves unto him knowingly or not.
Paul who was an apostle and wrote the book of Romans also wrote these verses. 1 Corinthians 9:27 But I keep under my body, and bring it into subjection: lest that by any means, when I have preached to others, I myself should be a castaway. And finally, here are some wise words of wisdom. Hebrews 4:1-2 Let us therefore fear, lest, a promise being left us of entering into his rest, any of you should seem to come short of it. For unto us was the gospel preached, as well as unto them: but the word preached did not profit them, not being mixed with faith in them that heard it. Some who hear will not endure unto the end. Matthew 10:22 And ye shall be hated of all men for my name's sake: but he that endureth to the end shall be saved. Paul wrote this to Timothy in the second chapter and letter to him. Therefore I endure all things for the elect's sakes, that they may also obtain the salvation which is in Christ Jesus with eternal glory. It is a faithful saying: For if we be dead with him, we shall also live with him: If we suffer, we shall also reign with him: if we deny him, he also will deny us: If we believe not, yet he abideth faithful: he cannot deny himself. Hebrews 10:35-39 Cast not away therefore your confidence, which hath great recompence of reward. For ye have need of patience, that, after ye have done the will of God, ye might receive the promise. For yet a little while, and he that shall come will come, and will not tarry. Now the just shall live by faith: but if any man draw back, my soul shall have no pleasure in him. But we are not of them who draw back unto perdition; but of them that believe to the saving of the soul.
But we who love God will never walk away because there's no other place to go to. John 6:68 Then Simon Peter answered him, Lord, to whom shall we go? thou hast the words of eternal life. Jesus alone can provide eternal life. John 14:6 Jesus saith unto him, I am the way, the truth, and the life: no man cometh unto the Father, but by me. So apply His command and saving name to all things in this life, to be counted worthy to obtain eternal life in the next. Colossians 3:17 And whatsoever ye do in word or deed, do all in the name of the Lord Jesus, giving thanks to God and the Father by him. Acts 4:12 Neither is there salvation in any other: for there is none other name under heaven given among men, whereby we must be saved. 2 Thessalonians 1:11-12 Wherefore also we pray always for you, that our God would count you worthy of this calling, and fulfil all the good pleasure of his goodness, and the work of faith with power: That the name of our Lord Jesus Christ may be glorified in you, and ye in him, according to the grace of our God and the Lord Jesus Christ.