Why John the beloved's writings are so unique

John writes uniquely, composing Gospel of John, several epistles, and the book of Revelation, because he has been blessed to a ministering angel as a flaming fire on the earth until the second coming of Christ upon request recorded in D&C 7:1-6. 

His great love for the Savior began before Jesus Christ's public ministry, for he was a disciple of John the Baptist.

"And the Lord said unto me: John, my beloved, what desirest thou? For if you shall ask what you will, it shall be granted unto you. 

And I said unto him: Lord, give unto me power over death, that I may live and bring souls unto thee. 

And the Lord said unto me: Verily, verily, I say unto thee, because thou desirest this thou shalt tarry until I come in my glory, and shalt prophesy before nations, kindreds, tongues and people.

And for this cause the Lord said unto Peter: If I will that he tarry till I come, what is that to thee? For he desired of me that he might bring souls unto me, but thou desiredst that thou mightest speedily come unto me in my kingdom. 

I say unto thee, Peter, this was a good desire; but my beloved has desired that he might do more, or a greater work yet among men than what he has before done. 

Yea, he has undertaken a greater work; therefore I will make him as flaming fire and a ministering angel; he shall minister for those who shall be heirs of salvation who dwell on the earth." (D&C 7:1-6)