We have to believe first as faith comes by hearing the gospel preached to us. If we do not believe the gospel that was preached to us then that means we do not believe, have no faith and will never be joint heirs with Christ.
No one was saved prior to Christ death and resurrection until the day of Pentecost where Jesus told the disciples to wait for the indwelling of the Holy Spirit before they were sent out into the world to preach the Gospel. Faith comes by hearing when we first believed in Christ.
I don't recall the details of our original discussion and I'm not going to retrace it through all of the posts now.
However, from what I can determine from the above, I had referenced Romans, which occurred after Acts timewise, didn't it? So, I'm not sure now of what your point is?
Pentecost represented the beginning of the latter rain - the beginning of the timeframe when the bulk of people would start to be saved. Christ's statement that "it is finished" on the cross
tells us that, at that point, all required for salvation was completed. If it was finished, well, it was finished. It was then the Holy Spirit began to indwell the elect, although He had also been with people before then.
[Jhn 19:30 KJV] 30 When Jesus therefore had received the vinegar, he said,
It is finished: and he bowed his head, and gave up the ghost.
Anyway, our belief comes as a fruit of the Spirit as a result of being born-again. So, faith is a byproduct and
a gift from God, not a cause.
[Gal 5:22 KJV]
22 But the fruit of the Spirit is love, joy, peace, longsuffering, gentleness, goodness,
faith,
[1Pe 1:5 KJV]
5
Who are kept by the power of God through faith unto salvation ready to be revealed in the last time.
[1Pe 1:20-21 KJV]
20 Who verily was foreordained before the foundation of the world, but was manifest in these last times for you,
21
Who by him do believe in God, that raised him up from the dead, and gave him glory; that your faith and hope might be in God.
[Gal 2:16 KJV]
16 Knowing that a man is not justified by the works of the law,
but by the faith of Jesus Christ, even we have believed in Jesus Christ, that we might be justified by the faith of Christ, and not by the works of the law: for by the works of the law shall no flesh be justified.
To be an "heir" one has to be the beneficiary of a will and testament. God did not use words loosely in the bible. It was by God's will and testament, that His beneficiaries were established, and they are those who are to become saved/born again. As with any will and testament, once the testator is dead, it cannot be changed (including its beneficiaries) - it is eternal. Their inheritance is God Himself.
[Heb 9:15-18 KJV]
15 And for this cause he is the mediator of the
new testament, that by means of death, for the redemption of the transgressions [that were] under the first testament, they which are called might receive the promise of eternal inheritance.
16 For where a testament [is], there must also of necessity be the
death of the testator.
17 For a testament [is] of force after men are dead: otherwise it is of no strength at all while the testator liveth.
18 Whereupon neither the first [testament] was dedicated without blood.
[Gal 4:7 KJV]
7 Wherefore thou art no more a servant, but a son; and if a son,
then an heir of God through Christ.