3 Nephi 23: 6 And now it came to pass that when Jesus had said these words he said unto them again, after he had expounded all the scriptures unto them which they had received, he said unto them: Behold, other scriptures I would that ye should write, that ye have not.
7 And it came to pass that he said unto Nephi: Bring forth the record which ye have kept.
8 And when Nephi had brought forth the records, and laid them before him, he cast his eyes upon them and said:
9 Verily I say unto you, I commanded my servant Samuel, the Lamanite, that he should testify unto this people, that at the day that the Father should glorify his name in me that there were many saints who should arise from the dead, and should appear unto many, and should minister unto them. And he said unto them: Was it not so?
10 And his disciples answered him and said: Yea, Lord, Samuel did prophesy according to thy words, and they were all fulfilled.
11 And Jesus said unto them: How be it that ye have not written this thing, that many saints did arise and appear unto many and did minister unto them?
12 And it came to pass that Nephi remembered that this thing had not been written.
13 And it came to pass that Jesus commanded that it should be written; therefore it was written according as he commanded.
The Lord works in mysterious ways. If you feel prompted to write, then you should do so. We may not know what purpose it will serve, we may not even live to see the effects of what we have written. But, none of us ever want to hear the Lord say: "I sent you a miracle. Why was it not written?"