The heading for this section explains that Joseph Smith and Oliver Cowdery asked if John the Beloved had died or had been permitted to live until the Second Coming. It further explains that the verses to follow are a translation of a record written—and subsequently squirreled away—by John himself.
First of all, this seems like a silly thing to consult God about. It's an almost irresponsible use of the Urim and Thummim. It's 1829 and the church hasn't even been officially established. The Book of Mormon isn't finished and no priesthood authority has been restored. With the breadth of doctrine still uncodified and the scope of theologies still unresolved, why the hell are these guys wasting time by asking whether or not one of Jesus's original disciples is immortal? What kind of religious concept has less bearing on the grand scheme of things? What could be less relevant to our salvation? They're in the middle of revealing scripture that has not seen the light of day in modern times and they're asking God to clarify a few vague New Testament verses that only apply to one guy? Seems frivolous.
Second, why are we even calling this a translation? Joseph Smith didn't have John's hidden record and—assuming this record existed—he was probably a continent or two away from it. Maybe the contents of the writing were revealed to him in his own language, but in order for this to have been a translation, God would have needed to reveal the words to Joseph in their original form and then have him use his seer stone or his Urim and Thummim to translate it into English. I refuse to believe a perfected being would be so inefficient. Although, God did make his ancient prophets go through a whole lot of effort to preserve a Book of Mormon record that didn't even need to be uncovered or in the same room as the translator to be converted into English (which I guess is pretty consistent with this translation story too), so maybe God is just grossly uneconomical with his prophets' time.
But moving onto the actual substance of this section, what we have here is a disagreement between Jesus and Alma. Because Jesus basically explains that Peter's desire to come speedily to Heaven was good, but that John's desire for immortal missionary service was even better [verses 5-6]. But the Book of Mormon prophet Alma clearly states in Alma 29:1-3 that his desire to be an angel to cry repentance to every people is sinful because he "ought to be content with the things the Lord hath allotted unto [him]."
And I suppose there may be an argument here that these are slightly different situations, but it's pretty clear to me that Alma's and John's motivations and objectives are identical, especially since, in verse 6, Jesus says he will make John "as a flaming fire and a ministering angel." How much more similar can these two guys' goals get? Yet the scriptures teach that one is awesome and one is sinful. That's kind of confusing.
Also there's a little sneak foreshadowing in this section about the restoration of the Priesthood through Peter, James, and John, but there will undoubtedly be more on that later.