When is man changed into immortal beings? Good question. You'll hear different answers, depending on who you ask.
Paul says it is at our resurrection, at the last trumpet.
1 Corinthians 15:52 in a moment, in the blink of an eye, at the last trumpet. For the trumpet will sound, and the dead will be raised imperishable, and we will be changed.
How? Paul records this question and answer too:
1 Corinthians 15:35, 38, 42, 45 (LEB)
But someone will say, “How are the dead raised? ...
Answer=
God gives to it a body just as he wishes, and to each one of the seeds its own body. ...
Notice, Paul says God does this as He wishes. And the “each one” includes Adam. Paul goes on to say
even the first Adam was not immortal!
Thus also is the resurrection of the dead. It is sown in corruption [i.e. Buried to decay], it is raised in incorruptibility. [i.e. immortal as he says above]
Thus also it is written, “The first man, Adam, became a living soul”; the last Adam became a life-giving spirit.
If you read all of 1 Cor 15, with an open mind, you’ll get what Paul is saying.
Christ is the only one to give immortality to men (including Adam, since He is God he's capable of that) and Christ will give Adam/Eve immortality at the trumpet sound (because Adam was a man needing a savior and Tree of Life just like the rest of us who are "in Him".
The idea that Adam has immortality already (or had it and lost it is Platonic thought and the lingering influence of that philosophy that influenced the church. The idea that man had immortal souls didn’t even appear in the teaching of the church fathers until around Tertullian’s time and culture. I have not found any early Apostolic Father that teaches that man is immortal (soul or otherwise) and it's certainly not in the bible. Maybe you've noticed how people point to Scriptures that are not even on the topic of man's spirit to teach about man's immortal spirit. Or they simply assume men's spirits are immortal because angels don't die.
Irenaeus plainly says that man is mortal (soul and all) and even says that Adam was mortal as well. He says this is why Paul claim's Christ is the 'second Adam'. I tend to think he was right.
He summarizes a long and complex argument with: “how could a man have learned that he is himself
an infirm being, and mortal by nature, but that God is immortal and powerful, unless he had learned by experience what is in both?”
On the otherhand,Tertullian will answer your question by this quote from his writings:
For some things are known even by nature: the immortality of the soul, for instance, is held by many; the knowledge of our God is possessed by all. I may use, therefore, the opinion of a Plato, when he declares, "Every soul is immortal."
Tertullian says that it’s just “natural” to think the soul is immortal. Really? I think not.
He says this belief is “held by many”. Yes I think he’s probably right about that but that’s not really a very good logical argument. Given what Paul says or Jesus (Matt 10:28) says, I don’t believe him.
He quotes Plato’s writings for his ‘scripture’.
I know that sounds far-fetched for a church father such as Tertullian to quote Plato for his evidence and sound like I’m making it up (as some have accused me of in the past). But I’m not. Go check out Tertullian’s writings and judge for yourself.
http://www.earlychristianwritings.com/text/tertullian16.html
http://www.earlychristianwritings.com/text/irenaeus-book5.html
Irenaeus’ argument using Paul’s 1 Cor 15 message is found in Chapter 3 but there’s also a good section in chapter VII: Inasmuch as Christ Did Rise in Our Flesh, It Follows that We Shall Be Also Raised in the Same; Since
the Resurrection Promised to Us Should Not Be Referred to Spirits Naturally Immortal, But to Bodies in Themselves Mortal.
I think Irenaeus means angels don’t die and I agree with him since they don’t have bodies to begin with. But he’s also saying that our resurrection (where we are made immortal) has nothing to do with spirits (angels) being naturally immortal.
Also, Chapter VI is a good one for this three part man (body/soul/spirit) discussion if you care what someone like him thinks about it. I tend to agree with Irenaeus’ points there. But it’s a deep discussion. I try not to pick just one verse out of the bible to prove man has either two or three parts since you could also pick a verse that says man has a ‘heart’ and add a fourth part, etc. It’s one of those things that are not so clear in the bible as people tend to think it is. They all have their favorite verses,
But I certainly agree that man has an immaterial part that goes to be with the Lord at the body’s death and a material part that returns to dust. I think the Bible as a whole uses ‘spirit’ in several different ways and is also translated from many different Hebrew and Greek words so it is difficult to discern.