Rom 5:10
10 For if, when we were enemies, we were reconciled to God by the death of his Son, much more, being reconciled, we shall be saved by his life.
All for whom Christ died, have been reconciled to God, by His death alone, not by their obedience, not by their faith, not by their repentance, but even while they were being enemies, unbelievers, children of wrath as others BY NATURE, now if this be the case, their being reconciled, they cannot be under condemnation and wrath as others Jn 3:18,36 even while being unbelievers !
You see, they cannot be both condemned and under wrath as enemies and reconciled to God as enemies at the same time !
Please consider
OT believers already declared righteous in promise by faith, like Abraham (Romans 4:3), as true OT believers ("foreknew" by God by their OT faith), predestined to believe the Gospel (Romans 8:28-29), were only legally reconciled to God by the death of Jesus on the cross (Romans 3:25-26). Even Abraham, while credited with righteousness by faith, and foreknown by God as a true OT believer, and given the right to become a Son of God in promise (John 1:12-13), to be born again [in Christ], was technically still in Adam and an enemy with God in the legal sense, according to the Law, up until Pentecost, when the Church was birthed [the first placed into Christ]. There sins were covered, but not yet atoned.
In short, consider that true OT believers still needed to be reconciled to God through Christ, even the ones in Abrahams bosom waiting for the cross who were owed that promise, yet died without receiving it (Hebrews 11:39-40). The life didn't happen until the indwelling. The Holy Spirit, the life, was not given until after the death resurrection and ascension of Jesus.
Consider the whole thrust of the book of Romans, written just 25 years after Pentecost, then the "we" in Romans 5:10, like in other places in Romans, is speaking to people who believed both before and after the cross. Having lived through that transition recorded in Acts, were true OT believers, some having heard the Gospel before the cross, sometimes from Jesus Himself, and believed and were owed the Holy Spirit of promise, the indwelling, the baptism/placing into with the Holy Spirit. There were also true OT believers, like Cornelius and his household, Lydia, and many others in Acts who were true OT believers already declared righteous by faith, just like Abraham, and did not hear the Gospel until after the death, resurrection and ascension of Jesus. They were predestined to be conformed to Christlikeness per (Romans 8:28-29). These are possibly what Paul had in mind when he said "we" in Romans 5:10. Not unbelievers as we know them today. But people in various states of faith, some who did not yet hear the Gospel, who were given to the Son by the Father, but not yet legally reconciled by their Gospel believing faith, which would place them into Christ. They were owed that reconciliation as a result of that 'placing into' Christ [indwelling] with the of the Holy Spirit that gives us all the ingredients that save/delivers us, both practically (born again), and legally (justified).
So the "we" in Romans 5:10 are, I believe, the saved in Promise by OT standards, but not yet legally reconciled NT believers. The reconciliation is just the promise answered. That's why the baptism/placing into with/by the Holy Spirit, the Holy Spirit is called the Promise of the Father. The promise was realized through the indwelling Holy Spirit, which had to wait until Christ was lifted up and glorified. So they ("we" in Romans 5:10) includes all believers who were owed that promise in faith, even the dead heroes of faith, who were perfected forever along with "us" ( True OT believers, who became True NT believers), (Hebrews 11:39-40).
That's the way I see Romans 5:10. Remember, Romans was written by Jews mostly for Jews. Most of them lived through the transition recorded in Acts, and many OT believers were trying to wrap their heads around all this stuff that's happening and being taught. Paul was explaining it all, grace and the Law, justification by faith, all of it. They had it all wrong. Paul was fixing that. Just something to consider.
Dave