JOEL - For one thing we don't just use the Bible. Our own scriptures, which we believe to also be the word of God along with the Bible, are helpful to us in understanding this doctrine. I'll get to that later.

God told Adam:

"Of every tree of the garden thou mayest freely eat: But of the tree of the knowledge of good and evil, thou shalt not eat of it: for in the day that thou eatest thereof thou shalt surely die."(Gen. 2:16-17)

But God also told Adam and Eve:

"Be fruitful, and multiply, and replenish the earth, and subdue it: and have dominion over the fish of the sea, and over the fowl of the air, and over every living thing that moveth upon the earth." (Gen 1:28)

Paul said that the fall of Adam was what brought death into the world:

"For since by man came death, by man came also the resurrection of the dead.
For as in Adam all die, even so in Christ shall all be made alive." (1 Cor. 15:21-22)

So according to God and Paul if Adam and Eve never partook of the fruit of good and evil they would not have died, remaining in the Garden of Eden forever as immortal souls. And in their innocent state it is very unlikely they knew anything about procreation.

A lot of what we know about this comes from some of our own scriptures. For example in the Book of Mormon we read:

"And now, behold, if Adam had not transgressed he would not have fallen, but he would have remained in the garden of Eden. And all things which were created must have remained in the same state in which they were after they were created; and they must have remained forever, and had no end.
And they would have had no children; wherefore they would have remained in a state of innocence, having no joy, for they knew no misery; doing no good, for they knew no sin." (2 Nephi 2:22-23)

How could they multiply and replenish the entire earth if they were stuck in the Garden of Eden and would not have any children there? And even if Adam and Eve were capable of having children while in the Garden and no one ever died, the Garden would have become very crowded in a very short time.

Another thing to consider is that the word "replenish" means "to fill or make complete AGAIN" (Am. Heritage Dict.). In Adam's case this would mean that he would have to fill the earth with plants, fish, fowls, and every living thing again, that were on the earth but for some reason are no longer there. The only way for those living things to no longer be on the earth is if they die. So why would God tell him to replenish the earth when at the time He said this nothing could die?

It is logical that it was in the plans all along for Adam to take the fruit so they could go out into the world and multiply and replenish it as God commanded them to do. Adam and Eve were fully aware of this plan and were therefore eventually able to make the correct choice.
The concept of free agency and choice has been an eternal principle from the very beginning. God was not being deceitful with Adam with these two seemingly contradictory commands, He was just allowing Adam to make the choice to either stay in the Garden forever or to obey the greater command which would bring about God's plan for all mankind.
A possible example of this is in how we keep the Sabbath day holy. We have been commanded that we should do no work on the Sabbath day. Yet if we stop and help someone fix their car that has broken down on the highway on the Sabbath day, we are not commiting a sin. We have chosen to obey the greater law of loving and serving our neighbor.
God also said:

"Therefore shall a man leave his father and his mother, and shall cleave unto his wife: and they shall be one flesh."(Gen. 2:24)

After Eve was beguiled by Lucifer to partake of the fruit, Adam concluded that God’s command to remain with his wife was more important than His command to abstain from the fruit. Once again the choice between a greater and lesser law.