Here are some verses that I feel support OSAS.
Jerimiah 32:40 - And I will make an everlasting covenant with them, that I will not turn away from doing them good; but I will put My fear in their hearts so that they will not depart from Me.
If we understand the entire context of this verse we can possibly get a different idea. The idea behind the words 'so that' can be understood also as 'in order to' or 'for this purpose'. In other words, God put His fear in their hearts for the purpose of giving them strength to not depart from Him. This by no means implies that they absolutley could not depart from Him. Especially because we know that the children of Israel DID depart from God.
John 6:37 - All that the Father gives Me will come to Me, and the one who comes to Me I will by no means cast out.
Again, Jesus says clearly that those who come to Him, He will not cast out. This does not rule out the possibility of some who come to Him choosing to walk away.
You say we have assurance, but then you go to say that we can screw things up ourselves and stop believing. So, if that's possible then we really aren't assured of anything.
We are assured beyond a doubt that God will never initiate Himself the departing from His people. He will remain with them for as long as they remain with Him. As long as we remain in Christ, God will not only never leave us, but He will also protect us so that no outside forces could possibly take us from Him. There are far too many verses that indicate the conditionality of our salvation to be ignored. One obvious one is Col 1:21-23. Verse 21 reads "And although you were formerly alienated and hostile in mind, engaged in evil deeds", this describes the Colossians' (and every Christian's) former state. Verse 22: "Yet He has now reconciled you in His fleshly body through death, in order to present you before Him holy and blameless and beyond reproach", This relates to our present state. We are "now reconciled", i.e. no longer aliens and enemies, but in a saved state because of our faith in the gospel. Verse 23: "If indeed you continue in the faith firmly established and steadfast, and not moved away from the hope of the gospel that you have heard, which was proclaimed in all creation under heaven, and of which I, Paul, was made of minister." Whether or not we reach that final salvation is clearly conditioned upon whether we continue to believe in Jesus Christ. Verse 23 states this condition without question. "If indeed you continue in the faith..." The unavoidable conclusion is that we can choose NOT to continue in the faith. This would certainly not be the result of some lapse in God's protection, nor the triumph of any enemies power; it would simply be the individual's exercise of God's free will.
I think it is a horrible thought to think that those whom the BLOOD OF CHRIST has bought, those whom the Holy Spirit has regenerated, those whom the SOVEREIGN GOD has predestined to glory can fall from the grace of God.
It is a horrible thought! That is why we are cautioned all through the New Testament to remain in the faith. Please remember that even for those who fall from God's grace, it is NEVER the fault of God or a lack of His power or ability to keep us. It is solely because of our God given free will and ability to choose. However, if you accept the five points of Calvinism then this is really the issue anyway. Total depravity says that we are so depraved that we cannot make that choice, God must make it for us. But this is also unbiblical.
It may appear that someone has stopped believing in Christ, but then we never know the heart. We can't make these assumptions about man's ability to unsave themselves just by seeing someone who appears to have lost "their" salvation. We can only go by what the word tells us.
You couldn't be more right. There are many who 'appear' to have lost their salvation, but ultimately God will judge whether or not that is so. We can only go by what the word tells us which is that the possibility exists. If we suspect that someone is falling from grace or even just not walking in a manner that would be pleasing to God, then we have a responsibility as fellow brothers to restore him to the faith with love.
You also say, "assurance of salvation do not teach unconditional perseverance"
Doesn't assurance imply unconditionality. If something is conidtional then it is by no means assured. If something is assured then there are no conditions upon which that thing can exist. The only condition of salvation is entirely in the Lords sovereign choice of his people before the foudations of the world. For those who have been Choosen by Him, they are no conditions. They will not fall from Christ, His love doesn't let us go as the scripture says.
This all depends upon your understanding of assurance. Every aspect of salvation has two parts, God's and man's. Man must respond to God's offer of salvation or, in other words, man must accept God's gift of salvation. Assurance in our salvation from God's perspective is unconditional. God is not restricted. He will do His part without fail in every case. However, to receive salvation, there are certain criteria placed upon us. This in no way takes away from God's sovereignty, as God has the sovereign ability to allow His creation to have free will. It also does not take away from God's grace because salvation is dependant upon His grace. He did not have to offer it to us at all. Yet He did because of His amazing love for us. The fact that we have conditions placed upon us does nothing to God's grace. Even under His pronounced conditions, we are still receiving something we will never deserve. That is God's grace.
If a Christian is lost and goes to hell, then didn't Christ lose that individual? If that individual was bought by the blood of Christ and is His child and that individual falls away and perishes, doesn't that show that Christ failed to "lose nothing"? The scripture is clear, we won't be lost, we will be raised up at the last day!
No, Christ did not lose that individual. They chose to walk away from the truth. Jesus Himself taught us this. Look at John 15:1-6. Here Jesus is discussing those who are already in a saved state; they are branches that are "in Me" (v. 2), fully attached to the life-giving vine. But Jesus exhorts these branches to "abide in Me" (v. 4), clearly implying that whether we abide or remain in the vine is our own responsibility. Verse 6 clearly shows that it is possible for one to choose NOT to abide in Christ: "If anyone does not abide in Me..." If anyone makes this choice, two things follow. First, the one who does not abide in Christ (i.e. ceases to believe) "is thrown away as a branch and dries up". The expression "thrown away" is
eblethe exo, literally, "thrown outside". He was at one time inside-inside the church, inside the love of God, inside the circle of grace; but now he is outside, excluded form grace, as the result of his own initiative, not God's. Second, those who choose to stop believing and who are thus excluded from grace are finally condemned to hell; "They gather them, and cast them into the fire and they are burned." This is not equivalent to 1 Cor 3:15 where one's works are subjected to the test of fire, affecting only the believer's reward. Here the excluded branches themselves-the fallen ones- are burned. Christ will never fail. His finished work on the cross will always be enough for the salvation of all who believe and remain in Him. Those who do not will answer for themselves. It will not be the fault of Christ.