Many Christians have said of implied that that mortal life is a 'test' - but for me this word is wrong; and I find it clearer and more coherent to think of mortal life (of being incarnated in a mortal body and then dying) as an experience.
This fits with the fact that so many humans never make it out of the womb, and so many more don't get past being born, and more don't make it to the years of responsibility - the idea of life as a 'test' therefore only fits a minority of the humans who have lived.
But I can certainly see that the experience of a pre-mortal spirit being - for however brief a time, and even if only in the womb - incarnate and mortal and then dying, might be necessary, irreplaceable for spiritual progress.
By analogy, it seems that for Christ to become our saviour, the experience of mortal life and death was necessary.
This line of argument suggests that experiencing death is as important, as necessary, for the spirit as is experiencing incarnate mortal life.