God prepared this earth as a home for His children. Adam and Eve were chosen to be the first people to live on the earth (see Moses 1:34; 4:26). Their part in our Father’s plan was to bring mortality into the world. They were to be the first parents. (See D&C 107:54-56.)
First, let me note that the only change made to this paragraph in the updating of the text was that the reference to Moses 4:26 was added to the reference to Moses 1:34. Though that might appear to be minor, it is the first of a series of connected changes made to this lesson in particular: if one looks at the two passages (1:34 and 4:26), it is clear that the second one was added in order to balance Adam with Eve. (That is, the older version made the claim that “Adam and Eve were chosen to be the first people to live on the earth” but only cited a scripture that describes Adam as the first man; by including Moses 4:26, there is also a scriptural citation that mentions Eve as being the mother of all living.) This balancing of what was before a primarily patriarchal manual will be at work throughout the lesson.
Interestingly, this paragraph served as an entire section in the earlier version of the manual, presumably because it alone deals with the idea of planning for earth. (The next two paragraphs, now a part of the same section, fell under a section titled “Adam and Eve Were Valiant Spirits.”) It seems that the whole first page of the lesson as it stands now has been grouped together because it all deals with the premortal, broadly speaking.