"Wherefore, the Lord hath commanded me to make these plates for a wise purpose in him, which purpose I know not.
But the Lord knoweth all things from the beginning; wherefore, he prepareth a way to accomplish all his works among the children of men; for behold, he hath all power unto the fulfilling of all his words. And thus it is. Amen."
It may have seemed a little strange to Nephi to have the Lord ask him to make a second record on a different set of plates when he had already kept a full record of his people. But he had learned to trust the Lord because He "knoweth all things from the beginning," and if the Lord said the second record was necessary, Nephi did not doubt Him. Nephi did not live to see the Lord's purpose accomplished, but we can be sure he later learned what that purpose was and was grateful that he had chosen to be obedient.
We are often asked to do things that don't make much sense. Instead of doubting the Lord, though, we should do our best to obey Him. Someday we may see the purpose behind the task, or the purpose may, as in Nephi's case, come after we have left this life. No matter which it may be, we can be sure that the Lord has a reason for asking us to do things, to suffer things, to endure, and our lives and the lives of others will be blessed for our obedience.