Romans 8:23 (ESV) "And not only the creation, but we ourselves, who have the firstfruits of the Spirit, groan inwardly as we wait eagerly for adoption as sons, the redemption of our bodies. 24 For in this hope we were saved. Now hope that is seen is not hope. For who hopes for what he sees? 25 but if we hope for what we do not see, we wait for it with patience."To understand, since Paul's wisdom, spirituality, discernment and intelligence was so profound, several concepts here must be explained. By the way, there has been no other theologian, philosopher nor sage who ever spoke with the elegance or wisdom as did Paul. This onetime murderer, stubborn zealot, and hater, had his life turned around by being born-again, not of his own doing, but the very grace of Jesus Christ! His salvation was genuine, and he was born-again in spite of himself. As such Paul's conversion seemed to be the very ideal of Calvinism, but Paul was a special case. (More on that someday).
First off, it's necessary to know what "first fruits" are in scripture. Of course in life, they are the best specimens of the harvest. They were gathered with the intention of having a special use. Even sacrificing a child to Molech was a pagan first fruit. First fruits were usually gathered as religious offerings. The ancient Hebrews gathered the best of their crops before they had their own, as an offering to JHVH. The amount of the first fruits for the Hebrew people was their tithe, or tenth portion. It belonged to God and God wasn't to get the remnants of the crop left over after the harvest, but the best at the beginning of the harvest. As such, first fruits were a measure of obedience, generosity, sacrifice and love.
When Cain brought of his harvest of the ground, God gave it little regard (Genesis 4:4), not because it was grain, but because it wasn't of the first fruits. We know that because Abel's offering was the first born, the first of his living crop. Hence, his offering was first, living, generous and sacrificial. It was symbolic of presenting himself as a living sacrifice, which is holy, acceptable and reasonable (Romans 12:1). In other words the first born is our very selves as children of God and believers in Christ Jesus.
In fact Jesus was the first fruit to be raised from the dead. He is God's own living sacrifice of his first fruit since Jesus was first, but was God's only Son, not as a created son, but the first to be sacrificed. (1 Corinthians 5:20). Jesus was the first to be raised from the dead because he was the first fruit of those who had died (put asleep). Because Jesus died and was resurrected so can we be! In fact Jesus sacrificed himself for our salvation, and his Ghost came down to fill Christians commencing on Pentecost after his ascension.
Hence, the recipients of the Holy Ghost have received a portion of the first fruit, (i., e., Jesus Christ).
At the resurrection are bodies will be redeemed to join our souls already enjoying eternity, thanks to Jesus. When our bodies and spirits are reunified, Christians become glorified. As such dead Christians are alive again with immortality, perfect health, sinless attributes and breath in the glory of God, the atmosphere of heaven. God cleans them enough that they can see him face-to-face!
Those whose bodies are glorified are adopted by God. We are his heirs and co-heirs with Jesus Christ. Like Jesus, we become first fruits. This adoption is our hope. All our lives after being born-again is this hope coming about. With the new birth, we're not yet saved, but have the hope of salvation since it's an unseen condition. Christians are not there yet, but with faith, have a vision of the day when they are glorified as sons of God!
Of course those who have the least doubt and are more certain of their faith are "saved". Their hope is profound enough that their vision of a future time is assured. Dropping the "hope of" from "the hope of salvation" is an implication that they have little doubt. Indeed, my faith is enough that I am saved even though I have yet to experience glorification! Because of the word of God, I accept his promise as fact because there is no other explanation for existence.
I don't see glory yet. I know it's there because God said that it is! I can't explain glory, but have faith that God's grace is sufficient for me to someday be glorified, and glorification is the instant that we are saved! Until then I am in an abstract spiritual situation: because I can't save myself, or self-glorify, I must depend on God to do that! There is no other recourse!
There is something which I must DO in order to be saved. Calvinists neglect it with sola gratia (grace alone). I must have the work of faith, but even my ability to do that work is a gift of God. It seems abstract, but just as I can breathe on my own, God designed me to breath. Hence, even breath is a gift although it is me who breathes. Faith is breathing God's Holy Spirit. It's there, but we must put it to use!