First off, I would completely agree with most Calvinists that the process of conversion is solely that of God alone. The reason for this is that I believe the Scripture if crystal clear on this matter, and in no place can that be more clearly seen than a place such as Ephesians 2:1-10.
Secondly, I would have to say that whenever anyone enters into glory, it will be due to no work of their own whatsoever. From the creation work of the Father, to the redeeming work of the Son, to the sanctifying work of the Holy Spirit (as laid out in the apostles creed), the whole process of salvation is totally and purely monergistic from beginning to end. As far as Biblical references for this argument, they are simply too numerous and widespread to mention here.
With all that said however, I have come to the conclusion now that, although saving faith is itself a gift of God and something we cannot create of our own volition, it is also something that we can come to lose or reject. Repeatedly throughout the New Testament we are warned about the dangers of false teachings and the deceitfulness of sin, and we are exhorted to constantly seek after Christ and His Gospel. What is more, we are warned and exhorted in this manner because we are His children by faith in Christ, and by heeding these warnings and exhortations we shall endure to the end, by the power of the Holy Spirit.
As an ex Calvinist myself, many of the warnings and exhortations mentioned above were things I viewed in a pretty much hypothetical sense for the true believer, rather than a real and present danger. The more I have looked however, the more I realise this is untrue. A prime example of what I mean would be to look at the letter to the Colossians.
Colossians 1:1–3 (ESV)
1 Paul, an apostle of Christ Jesus by the will of God, and Timothy our brother, 2 To the saints and faithful brothers in Christ at Colossae: Grace to you and peace from God our Father. 3 We always thank God, the Father of our Lord Jesus Christ, when we pray for you,
The opening address is clearly written to the "saints and faithful brothers in Christ". This is not to say that when the letter was read in the churches, every hearer would be regenerate. But rather that the content of the message written by Paul under the inspiration of the Holy Spirit, was directed to those truly in the faith.
Immediately following, Paul goes on to remark on the obvious fruits of faith that have been manifest amongst the Colossian believers, and how they had heard and believed the true Gospel message, being taught by his faithful fellow servant, Epaphras. I think it really would be a leap of foolishness to suggest who Paul is indeed writing to are anything but genuine, regenerate Christian believers.
Paul then goes on to speak about the pre-eminence of Christ, and how in Him the fulness of God dwells, having the power and authority to reconcile to Himself all things in heaven and on earth by the blood of His cross. Then comes the kicker:
Colossians 1:21–23 (ESV)
21 And you, who once were alienated and hostile in mind, doing evil deeds, 22 he has now reconciled in his body of flesh by his death, in order to present you holy and blameless and above reproach before him, 23 if indeed you continue in the faith, stable and steadfast, not shifting from the hope of the gospel that you heard, which has been proclaimed in all creation under heaven, and of which I, Paul, became a minister.
What this shows is that our full redemption is actually conditional. That condition being that we believe, and continue to believe in the faith once for all delivered to the saints. Is that not the prime reason for such harsh warnings against false teachers, promoting a false gospel that can never save?
Once again, as an ex Calvinist I would often refer to the "golden chain of redemption" in Romans 8:29-30 as evidence backing up the perseverence of the saints, for it is spoken in the past tense as if already a done deal so to speak. However even written only a few verses previously, and obviously directly related to verses 29-30, Paul writes:
Romans 8:16–18 (ESV)
16 The Spirit himself bears witness with our spirit that we are children of God, 17 and if children, then heirs—heirs of God and fellow heirs with Christ, provided we suffer with him in order that we may also be glorified with him. 18 For I consider that the sufferings of this present time are not worth comparing with the glory that is to be revealed to us.
These verses are those leading directly leading into Paul speaking about the future glory in Christ that climaxes in verses 29-30, and place a clear condition the final glorification of the believer.
My reason for joining this conversation is not to jump on Calvinism though, as I feel much closer to Calvinist theology than any other. Rather my reason is that I believe that in this doctrine, Calvinism tries to force out assurance of salvation in a slightly off centre way. The reliance is upon the sovereign will of God that will not be fully unveiled before the Last Day. It is this crucial point that I have in hindsight often tried to argue for from the text of Scripture, where in reality it is not truly given to us.
As a Lutheran I have come to realise the value of Word and sacrament in the Christian life, as the channels through which we receive the promises of God's grace in Christ crucified and risen again. For God has instituted clear and tangible means, through which we can find full assurance of faith, without having to look under every rock and crevice to find it.
We can willingly submit ourselves to hearing His Word preached and expounded, knowing that by it our faith will grow:
Romans 10:17 (ESV)
17 So faith comes from hearing, and hearing through the word of Christ.
We can know without doubt that we are in Christ through the gift of baptism, believing that through it we share in both His death and resurrection life:
Romans 6:3–5 (ESV)
3 Do you not know that all of us who have been baptized into Christ Jesus were baptized into his death? 4 We were buried therefore with him by baptism into death, in order that, just as Christ was raised from the dead by the glory of the Father, we too might walk in newness of life. 5 For if we have been united with him in a death like his, we shall certainly be united with him in a resurrection like his.
As we partake of His Body and Blood in the bread and cup, we are reminded to the depth of our being that He gave Himself completely for the forgiveness of our sins, sealing our redemption as a covenant in His own blood:
1 Corinthians 11:23–26 (ESV)
23 For I received from the Lord what I also delivered to you, that the Lord Jesus on the night when he was betrayed took bread, 24 and when he had given thanks, he broke it, and said, “This is my body, which is for you. Do this in remembrance of me.” 25 In the same way also he took the cup, after supper, saying, “This cup is the new covenant in my blood. Do this, as often as you drink it, in remembrance of me.” 26 For as often as you eat this bread and drink the cup, you proclaim the Lord’s death until he comes.
I could continue, but I think my point is clear by now. The full assurance of our salvation is found solely in the Person and Work of Jesus Christ, which has been given to us in the Scripture. The Old Testament speaking prophetically concerning the coming Messiah, and the doctrine of the Apostles recorded in the New Testament, revealing how Christ is the fulfillment of the Scripture.
Thankfully, the conditions spoken of earlier concerning our ultimate glorification, are not works of our own. If that were the case we would all be lost forever. Rather it is a natural fruit borne from someone who has come to an understanding of their predicament, as a sinful wretch who should rightfully be eternally condemned by a Holy, Righteous and Almighty God. Who understands that should they be delivered from that dreadful place, it can only be because of His mercy and grace. The promise of which being embodied in the Person and Work of the only Redeemer, Jesus Christ.
I think the Bible is pretty clear that if the above is true of a Christian believer, even if that understanding is almost like a distant memory, there remains hope of salvation. For God is able once again to grant them the gift of repentance and faith. However I also believe the Bible speaks of a point of no return, where someone who once believed can totally reject the faith, and God will solidfy their rejection of Him to their eternal destruction:
Hebrews 10:24–31 (ESV)
24 And let us consider how to stir up one another to love and good works, 25 not neglecting to meet together, as is the habit of some, but encouraging one another, and all the more as you see the Day drawing near. 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.
2 Thessalonians 2:9–12 (ESV)
9 The coming of the lawless one is by the activity of Satan with all power and false signs and wonders, 10 and with all wicked deception for those who are perishing, because they refused to love the truth and so be saved. 11 Therefore God sends them a strong delusion, so that they may believe what is false, 12 in order that all may be condemned who did not believe the truth but had pleasure in unrighteousness.