Literary: The break in the verses here creates an artificial break in a nicely turned phrasing in Moroni’s discourse. To reconstruct the context, note how the argument flows:
Behold, all ye who are despisers of the works of the Lord, for ye shall wonder and perish. O then despise not, and wonder not, but hearken unto the words of the Lord
The reference is to those who are “despisers of the works of the Lord.” These will “wonder and perish,” and certainly the perishing is not a desirable end. Therefore, Moroni admonishes them to “despise not, and wonder not.” The way to avoid the destruction is simple, they need to “hearken unto the words of the Lord.” Those who had despised the Lord’s words must cease to do so, and embrace those words. The alternative is that they perish.
Moroni’s is not a message of gloom, promising destruction to the wicked, but rather a message of hope in repentance. Moroni does not leave the “despisers” without hope. Rather, he tells them that they can change, and that they can avoid the destruction. The can “work out your own salvation with fear and trembling before him.” For them, and for us, it is still not too late.