Alma 42:2 - 10

.... After the Lord God sent our first parents forth from the garden of Eden, to till the ground, from whence they were taken - yea, he drew out the man, and he placed at the east end of the garden of Eden, cherubim, and a flaming sword which turned every way, to keep the tree of life -

Now, we see that the man had become as God, knowing good and evil; and lest he should put forth his hand, and take also of the tree of life, and eat and live forever, the Lord God placed cherubim and the flaming sword, that he should not partake of the fruit -

And thus we see, that there was a time granted unto man to repent, yea, a probationary time, a time to repent and serve God.

For behold, if Adam had put forth his hand immediately, and partaken of the tree of life, he would have lived forever, according to the word of God, having no space for repentance; yea, and also the word of God would have been void, and the great plan of salvation would have been frustrated.

But behold, it was appointed unto man to die - therefore, as they were cut off from the tree of life they should be cut off from the face of the earth - and man became lost forever, yeah, they became fallen man.

And now, ye see by this that our first parents were cut off both temporally and spiritually from the presence of the Lord; and thus we see they became subjects to follow after their own will.

Now behold, it was not expedient that man should be reclaimed from this temporal death, for that would destroy the great plan of happiness.

Therefore, as the soul could never die, and the fall had brought upon all mankind a spiritual death as well as a temporal, that is, they were cut off from the presence of the Lord, it was expedient that mankind should be reclaimed from spiritual death.

Therefore, as they had become carnal, sensual, and devillish, by nature, this probationary state became a state for them to prepare; it became a preparatory state.