Here is a synopsis from the Monergism website:
REGENERATION - THE CHRISTIAN IS BORN AGAIN, by J.I. Packer
In reply Jesus declared, “I tell you the truth, no one can see the kingdom of God unless he is born again.” JOHN 3:3
"Regeneration is a New Testament concept that grew, it seems, out of a parabolic picture-phrase that Jesus used to show Nicodemus the inwardness and depth of the change that even religious Jews must undergo if they were ever to see and enter the kingdom of God, and so have eternal life (John 3:3-15). Jesus pictured the change as being “born again.”
"The concept is of God renovating the heart, the core of a person’s being, by implanting a new principle of desire, purpose, and action, a dispositional dynamic that finds expression in positive response to the gospel and its Christ. Jesus’ phrase “born of water and the Spirit” (John 3:5) harks back to Ezekiel 36:25-27, where God is pictured as symbolically cleansing persons from sin’s pollution (by water) and bestowing a “new heart” by putting his Spirit within them. Because this is so explicit, Jesus chides Nicodemus, “Israel’s teacher,” for not understanding how new birth happens (John 3:9-10). Jesus’ point throughout is that there is no exercise of faith in himself as the supernatural Savior, no repentance, and no true discipleship apart from this new birth."
"Elsewhere John teaches that belief in the Incarnation and Atonement, with faith and love, holiness and righteousness, is the fruit and proof that one is born of God (1 John 2:29; 3:9; 4:7; 5:1, 4). It thus appears that as there is no conversion without new birth, so there is no new birth without conversion."
... "Regeneration is monergistic: that is, entirely the work of God the Holy Spirit. It raises the elect among the spiritually dead to new life in Christ (Eph. 2:1-10). Regeneration is a transition from spiritual death to spiritual life, and conscious, intentional, active faith in Christ is its immediate fruit, not its immediate cause. Regeneration is the work of what Augustine called “prevenient” grace, the grace that precedes our outgoings of heart toward God."
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I am not sure what you would accept as knowledge of being "absolutely saved". If one defines it as having divine knowledge, then one has defined the concept out of human existence. I am speaking of human knowledge that is possible.
The objective criteria, then, for us to know for sure is found in the Bible. The are so many passages that say "when such and such happens, the person is saved". Jesus tells us Himself, in great detail, what a born again person looks like. He paints a portrait. As we are sanctified, the portrait becomes clearer. We look at ourselves to see if we look like that, and if we are honest, then we can know. As we grow it also helps us to recognize and then reckon when we stray.
Perhaps at the very beginning, many have nothing more than John 3:16, so that person believes he knows. That's OK, because the truly regenerated heart will seek to learn more and grow in the faith, EVEN THOUGH the beginner may very well have no idea about that yet.
And yes, this author does believe that Baptism is symbolic. It signifies what has already happened. Here is what the same author says about it:
BAPTISM - THIS RITE EXHIBITS UNION WITH CHRIST, by J. I. Packer
Or don’t you know that all of us who were baptized into Christ Jesus were baptized into his death? We were therefore buried with him through baptism into death in order that, just as Christ was raised from the dead through the glory of the Father, we too may live a new life. ROMANS 6:3-4
"Christian baptism, which has the form of a ceremonial washing (like John’s pre-Christian baptism), is a sign from God that signifies inward cleansing and remission of sins (Acts 22:16; 1 Cor. 6:11; Eph. 5:25-27), Spirit-wrought regeneration and new life (Titus 3:5), and the abiding presence of the Holy Spirit as God’s seal testifying and guaranteeing that one will be kept safe in Christ forever (1 Cor. 12:13; Eph. 1:13-14). Baptism carries these meanings because first and fundamentally it signifies union with Christ in his death, burial, and resurrection (Rom. 6:3-7; Col. 2:11-12); and this union with Christ is the source of every element in our salvation (1 John 5:11-12). Receiving the sign in faith assures the persons baptized that God’s gift of new life in Christ is freely given to them. At the same time, it commits them to live henceforth in a new way as committed disciples of Jesus. Baptism signifies a watershed point in a human life because it signifies a new-creational engrafting into Christ’s risen life."
"Christ instructed his disciples to baptize in the name of the Father, the Son, and the Holy Spirit (Matt. 28:19). This means that the covenant relation which baptism formally confers is one of acceptance by, communion with, and commitment to all three Persons of the Godhead. When Paul says that the Israelites were “baptized into Moses” (1 Cor. 10:2), he means that they were put under Moses’ control and direction. Thus, baptism into the name of the triune God signifies control and direction by God himself."
"The outward sign does not automatically or magically convey the inward blessings that it signifies, and the candidates’ professions of faith are not always genuine. Peter had to tell the newly baptized Simon Magus that he was still unrenewed in heart (Acts 8:13-24)".
Sounds a lot like Baptism, and not the "Sinner's Prayer" that regenerates someone, doesn't it? I believe the model in this subject, as in other Christian subjects, is Christ's own Baptism. When Christ was baptised with water, the Spirit came upon Him, as visibly portrayed by the dove. In a like manner, we realize that we, too, receive the gift of the Holy Spirit during the ritual of Baptism, the washing of regeneration, as the Scripture calls it.
Regeneration is monergistic: that is, entirely the work of God the Holy Spirit.
Of course it is. But it doesn't follow that we are not expected to respond to God's gift by repenting and converting. God gives us the ability to do it - we are told we are to do it (Jesus said: "{YOU} REPENT and BELIEVE" - Not "God Repents for you" or "God believes for you", or "Don't worry, your God has chosen all people standing among us as the elect. Believe or not, but you are still saved" or "It doesn't matter what you do, God has already chosen you, whether you do anything now or not")
I am not sure what you would accept as knowledge of being "absolutely saved". If one defines it as having divine knowledge, then one has defined the concept out of human existence. I am speaking of human knowledge that is possible.
Protestants make the claim that they know that THEY are IRRESISTIBLY SAVED! Men CANNOT EVER LOSE their salvation, no matter what they do! However, in case something in the future, say 40 years from now, happens to make them reject the faith, well, naturally, they weren't saved to begin with! That's your side's argument. Frankly, it isn't Biblical. You are trying to establish a knowledge as certain that IS NOT KNOWABLE in the absolute sense. Countless times, I have argued that we cannot know the distant future. Yet, you argue that we can know God's mind. And yet, if for some reason we DON'T know God's mind, then we never were abiding in Christ in the first place? What sort of an argument is that? Can you see the frustration this presents? Because one cannot know they will not fall away in the future - despite your pleading to the contrary today - your salvation today is insecure! Even today, you don't know you are saved, if you follow your argument all the way...
Let's say you are "saved" in 2000. All things go well with you. You are vibrant in the faith, you read the Scriptures, etc....There is no indication that you will fall away. In 2006, you argue that you are STILL saved, and will be saved forever... But let's say in 2010, you go on a trip to Africa to become a Christian missionary. You are so in love with Christ, you want to spread the Gospel to all. But after seeing the war, the famine, the starvation, the little kids dying in their mothers' arms daily, up close in person, you begin to question whether God really cares about man. Why should a little child have to die? Starve to death? What kind of God allows that? It is enough to shake the faith of many people. You might deny this, but only because you haven't seen it in person and up close. You might not like this scenario, but I have seen people who have undergone this very thing. They fell away from Christianity altogether because of what they saw while trying to be Christian missionaries.
Are you now going to try to tell me that this person WAS NEVER SAVED TO BEGIN WITH??? See where this leads you, brother? This person in 2006 thought he was saved, but in 2010, he is told he never was saved to begin with. HOW DO YOU KNOW THIS WON'T HAPPEN TO YOU? Or any other brother? No. Christians are saved, are healed. And Christians get sick spiritually again and need subsequent healing and salvation. That is the only Biblical interpretation of the entire Scripture. Not this idea you present, which logically leaves one with no true knowledge of even TODAY whether they are "healed" or "saved"... You don't even know if you are healed from your disease - as you say it might break out again - so you never were healed to begin with.
The outward sign does not automatically or magically convey the inward blessings that it signifies, and the candidates’ professions of faith are not always genuine. Peter had to tell the newly baptized Simon Magus that he was still unrenewed in heart (Acts 8:13-24)".
Baptism "works", but the person can allow God's grace to fall in vain upon him. Thus, the person has fallen back. He was healed, and has gotten sick again...
Regards