Moroni speaks directly to his future reader. While he wrote to future Lamanites, he certainly understood that the Book of Mormon would come to the gentiles as well, so we may suppose that they are included in this direct address.
[if it be wisdom in God that ye should read them]: Moroni is sealing up the plates. Not all of the people of the future will be able to read the text, only those after the time when God sees fit to reveal the text to mankind. It is this variable of timing that will determine whether it is in the “wisdom of God” that we should receive it. After the publication of the text, it depends upon our access to the Book of Mormon. At this point, the will of God is that all have the opportunity, and it is now in our hands to make that happen.
[that ye would remember how merciful the Lord hath been unto the children of men]: God has been merciful before, and Moroni is indicating that the privilege of reading the Book of Mormon is yet another indication of the mercies of God toward man.