Once saved always saved?

I believe in assurance of salvation, and not just "once saved, always saved," but also that those who belong to God are chosen by him before they came to faith, before they were created, even before the world was created, that's good assurance! Always saved...
 
And God will not lose any of them:
 
Eph. 1:4-6 "For he chose us in him before the creation of the world to be holy and blameless in his sight. In love he predestined us to be adopted as his sons through Jesus Christ, in accordance with his pleasure and will--to the praise of his glorious grace, which he has freely given us in the One he loves."
 
Rom. 8:29-30 "For those God foreknew he also predestined to be conformed to the likeness of his Son, that he might be the firstborn among many brothers.  And those he predestined, he also called; those he called, he also justified; those he justified, he also glorified."
 
Not "most of those he foreknew", "many of those he predestined", but all, every one.
 
1CO 1:8-9 He will keep you strong to the end, so that you will be blameless on the day of our Lord Jesus Christ.
2CO 1:21-22 Now it is God who makes both us and you stand firm in Christ. He anointed us, set his seal of ownership on us, and put his Spirit in our hearts as a deposit, guaranteeing what is to come.
2CO 5:5-6 Now it is God who has made us for this very purpose and has given us the Spirit as a deposit, guaranteeing what is to come. Therefore we are always confident...
 
And yet there are real warnings:
 
Hebrews 3:12  See to it, brothers, that none of you has a sinful, unbelieving heart that turns away from the living God.
The result spoken of in Hebrews, if people turn away, is not just loss of rewards! It is called falling, and then he describes the results:
Hebrews 4:11  Let us, therefore, make every effort to enter that rest, so that no one will fall by following their example of disobedience.
Hebrews 6:1-6  Therefore let us leave the elementary teachings about Christ and go on to maturity...  And God permitting, we will do so. 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.
 
Here it is clearly shown that it is impossible to be saved, lose your salvation, and then come back again. Yet even with this severest of warnings, comes assurance:
 
Hebrews 6:9  Even though we speak like this, dear friends, we are confident of better things in your case--things that accompany salvation.
 
So how can we understand these real warnings with these real assurances? Jesus makes a similar set of two statements:
 
Luke 12:4-7  "I tell you, my friends, do not be afraid of those who kill the body and after that can do no more. But I will show you whom you should fear: Fear him who, after the killing of the body, has power to throw you into hell. Yes, I tell you, fear him. Are not five sparrows sold for two pennies? Yet not one of them is forgotten by God. Indeed, the very hairs of your head are all numbered. Don't be afraid; you are worth more than many sparrows."
 
"Fear being thrown into hell, yet don't fear," we read. And this is spoken to believers, to those who by Jesus' own estimation, are his friends. Now we must by all means not take one set of verses and erase the other set with them. This does seem to happen in the "once saved, always saved" discussions: "Text A!" "Well text B!" "Well text A!" "Well text B!" And never the twain will meet.
 
But Jesus meant both, and so does the author of Hebrews, and so do the other writers such as Paul, when they give assurances, and when they warn, and they warn of much more than a loss of rewards.
 
It seems we have a mystery here, especially since we see the warnings and assurances so often right together, this is not some author forgetting what he wrote earlier, and contradicting himself in the very next sentence! What was a warning is next an assurance, and both must be real, and I don't really know how, only I would say that the prospects for disobedient Christians go farther down (while remaining Christians) than anyone expects! They should fear, yet they need not fear...
 
1 Corinthians 11:31-32  But if we judged ourselves, we would not come under judgment. When we are judged by the Lord, we are being disciplined so that we will not be condemned with the world.
 
1 Thessalonians 5:21-24  Test everything. Hold on to the good. Avoid every kind of evil. May God himself, the God of peace, sanctify you through and through. May your whole spirit, soul and body be kept blameless at the coming of our Lord Jesus Christ. The one who calls you is faithful and he will do it.
 
And then Paul says, "Brothers, pray for us"...

Scripture shows us that we can know we now have eternal life:
 
1 Jn. 5:13 I write these things to you who believe in the name of the Son of God so that you may know that you have eternal life.
 
Not temporary life! Eternal life, life forever. And 1 John has many ways to check:
 
1 Jn. 2:3 We know that we have come to know him if we obey his commands.
1 Jn. 2:29 If you know that he is righteous, you know that everyone who does what is right has been born of him.
1 Jn. 3:14 We know that we have passed from death to life, because we love our brothers.
1 Jn. 4:13 We know that we live in him and he in us, because he has given us of his Spirit.
 
This list leaves out a lot of such verses in 1 John! You could almost read the whole book as if it was addressing this topic...

"Are there few that be saved? If God does not hold up His people, if He does not keep them by His grace and power, they will be very few indeed—a child may count them, and, in fact, have none, not one, to count. We believe, and our hearts swell with high and holy joy in believing, that every child of man who loved God—every one of Adam's race who was renewed in heart—all who were ever on the Lord's side—will be found among the saved. Not one will be lost. Not one will be missed from the eternal banquet. Not one, will be outside the gates of the holy city. All, all shall be there, and there for ever, and ever, and ever!" (William O’Neill)

1JN 2:1 But if anybody does sin, we have one who speaks to the Father in our defense--Jesus Christ, the Righteous One.
 
"Yes, though we sin, we have Him still. John does not say, 'If any man sin he has forfeited his advocate,' but 'we have an advocate,' sinners though we are. All the sin that a believer ever did, or can be allowed to commit, cannot destroy his interest in the Lord Jesus Christ, as his advocate. He declares Himself my substitute and puts His obedience to my account. My soul, thou hast a friend well fitted to be thine advocate, He cannot but succeed; leave thyself entirely in His hands." (C.H. Spurgeon)

RO 6:8-11 Now if we died with Christ, we believe that we will also live with him. For we know that since Christ was raised from the dead, he cannot die again; death no longer has mastery over him. The death he died, he died to sin once for all; but the life he lives, he lives to God. In the same way, count yourselves dead to sin but alive to God in Christ Jesus.
 
"As Christ once dead dies no more, so in His members the life of grace cannot die totally."
 
2CO 5:5 Now it is God who has made us for this very purpose and has given us the Spirit as a deposit, guaranteeing what is to come.
 
"It is the earnest penny of our salvation, not the pawn or pledge, which is to be returned again. The earnest is a part of the bargain, and the first fruits of Heaven. Now the earnest would be lost if the bargain of salvation stand not, and he that hath the earnest be not saved; and if such an one be damned, he carries the earnest of the Spirit along with him into hell, which must needs be absurd." (Christopher Ness)
 
EPH 1:13-14 "And you also were included in Christ when you heard the word of truth, the gospel of your salvation. Having believed, you were marked in him with a seal, the promised Holy Spirit, who is a deposit guaranteeing our inheritance."
 
"They first believed and then were sealed, i.e., fully assured. God honours our sealing to His truth by His sealing with His Spirit; as the earnest makes the bargain, so the seal ratifies and confirms it. And the broad seal of Heaven must needs be more unalterable than that of the Medes and Persians."
 
"Saints are compared to a tree that fades not (Ps 1:3); to a cedar in Lebanon (Ps 92:12; Ho 14:5); to Mount Zion that cannot be moved but abideth for ever (Ps 125:1); and to a house built on a rock (Mt 7:24). Though they fall, God raises them up (Ps 37:24; Pr 24:16). The Lord is with them in their old age (Isa 46:4), and is their guide even unto death (Ps 48:14), so that they cannot totally and finally be lost." (Christopher Ness)
 
"Not as the world, the Saviour gives: He is no fickle friend; Whom once He loves, He never leaves, But loves him to the end.
Though thousand snares enclose his feet, Not one shall hold him fast; Whatever dangers he may meet, He shall get safe at last.
The spirit that would this truth withstand Would pull God’s temple down, Wrest Jesus’ sceptre from His hand, And spoil Him of his crown.
Satan might then full victory boast, The Church might wholly fall; If one believer may be lost, It follows, so may all.
But Christ, in every age, has prov’d, His purchase firm and true; If this foundation be removed, What shall the righteous do?"

"The worst possible that may be is, that ye leave behind your children, husband and the church of God in miseries. But ye cannot get them to heaven with you for the present. Ye shall not fail to see them, and Christ cannot miscount one of the poorest of His lambs. No lad, no girl, no poor one shall be a-missing in the day that the Son shall render up the kingdom to His Father." (Samuel Rutherford)

"I have, sometimes, when the Lord has assured me of His love, felt as if I could not contain more joy and delight. My eyes ran down with tears of gratitude. I fell upon my knees to bless Him, but rose again in haste, feeling as if I had nothing more to ask for, but must stand up and praise Him; then have I lifted my hands to heaven, longing to fill my arms with Him; panting to talk with Him, as a man talketh with his friend, and to see Him in His own person, that I might tell Him how happy He had made His unworthy servant, and might fall on my face, and kiss His feet in unutterable thankfulness and love. Such a banquet have I had upon one word of my Beloved, 'thou art Mine,' that I wished, like Peter, to build tabernacles in that mount, and dwell for ever."
 
"But, alas, we have not, all of us, yet learned how to preserve that blessed assurance. We stir up our Beloved and awake Him, then He leaves our unquiet chamber, and we grope after Him, and make many a weary journey trying to find Him. If we were wiser and more careful, we might preserve the fragrance of Christ's words far longer; for they are not like the ordinary manna which soon spoiled, but are comparable to that omer of it which was put in the golden pot, and preserved for many generations. The sweet Lord Jesus has been known to write his love-thoughts on the heart of His people in so clear and deep a manner, that they have for months, and even for years, enjoyed an abiding sense of His affection. A few doubts have flitted across their minds like thin clouds before a summer's sun, but the warmth of their assurance has remained the same for many a gladsome day. Their path has been a smooth one, they have fed in the green pastures beside the still waters, for His rod and staff have comforted them, and His right hand hath led them. In many a humble cot, in many a crowded workshop, in many a village manse there are to be found men of the house of David, men after God's own heart, anointed with the holy oil."
 
"It is, however, a mournful truth, that men of fearful mind and despondent heart are everywhere to be seen. Why is this? Can I not grow stronger? Must I be a mourner all my days? How can I get rid of my doubts? The answer must be: yes, you can be comforted, but only the mouth of the Lord can do it, for anything less than this will be unsatisfactory."   "I doubt not that there are means, by the use of which those who are now weak and trembling may attain unto boldness in faith and confidence in hope; but I see not how this can be done unless the Lord Jesus Christ manifest His love to them, and tell them of their union to Him. This He will do, if we seek it of Him. The importunate pleader shall not lack his reward. Haste thee to Him, O timid one, and tell Him that nothing will content thee but a smile from His own face, and a word from His own lips! Speak to Him, and say, 'O my Lord Jesus, I cannot rest unless I know that Thou lovest me! I desire to have proof of Thy love under Thine own hand and seal.' " (Spurgeon)

“Faith is not assurance. But this doth sometimes crown and reward a strong, vigorous and heroic faith; the Spirit of God breaking in upon the soul with an evidencing light, and scattering all that darkness, and those fears and doubts which before beclouded it.”—“Bishop Hopkins on the Covenants.”
 
J. C. Ryle, Holiness: Its Nature, Hindrances, Difficulties and Roots, p. 188.

"It is spoken also in Heb 6:5 of such as only taste, but digest not; that have their minds informed, not their hearts reformed; sanctified in profession, not in power. And the apostle was persuaded otherwise of these Hebrews to whom he wrote; he was convinced that their faith was not a historical one, but of the operation of God (Col 2:12), evidenced by their fruits, (Heb 6:9,10; 1Th 1:5)."
 
"We are elected unto obedience, through the 'sanctification of the Spirit' (1Pe 1:2); therefore God hath promised to sanctify those whom He purposed to save. We teach with Augustine that, 'Election is an ordaining to grace as well as to glory.' In pre-destination, therefore, the means of salvation are no less absolutely decreed than salvation itself. We may not conceive that God’s decree runs after this form, 'I will predestinate Peter to salvation, if it should so happen that he doth believe and persevere;' but rather thus, 'I do predestinate Peter to salvation, which, that he may infallibly obtain, I will give him both faith and perseverance.' Were it otherwise, the foundation would not stand sure; yea, and God’s gifts would not be without repentance, if God did not absolutely decree to give and bestow faith and perseverance to His elected ones. The covenant of grace runs in this tenure, 'I will be a God to you, and ye shall be a people unto Me' that is, I will make ye so." (Christopher Ness)