Unlike missionaries today, early missionaries did not focus much on the first vision. Instead, they preached from the Bible and the Book of Mormon. Historian Richard Bushman has pointed out that in the early 1800s, lots of people claimed to have visions, so Joseph's experience would not be all that unusual. That makes sense to me.
Another question that people ask is why Joseph and Oliver didn't include the first vision in the eight essays on Church history they wrote and published in 1834-5. The essays describe Joseph's concern about the welfare of his soul and his prayer, but instead of the first vision, they relate Moroni's first visit. From our perspective today, this would have been an ideal time for Joseph to set out the first vision. Why wait until 1838 to relate the vision in detail, and then delay the publication until the 1842 Times and Seasons?
Bushman's explanation could be one factor. Maybe in 1834-5, a vision of God was not so unusual. What set Joseph's experience apart from other spiritual experiences was the visit of a resurrected being who directed him to translate ancient records. Naturally, that would be the focus of the history.
Another explanation could be the law of witnesses. Joseph's first vision took place with him alone. Maybe he hesitated to relate that experience until he had a second witness, when someone could attest to a personal experience with Jesus Christ. That did not occur until April 3, 1836, when the Lord appeared to Joseph and Oliver together in the Kirtland temple, as described in D&C 110. (Prior to that, Joseph and Sidney Rigdon had shared a vision during which they saw and conversed with Christ (D&C 76), but that vision was described as less physical than the experience in the Kirtland temple, when they described the Lord standing on the pulpit and provided a detailed description of his appearance.)
One aspect of the first vision the manual discusses is the existence of four separate accounts. Anyone who has described an experience in their lives more than once, especially over a period of years, knows that we don't relate experiences the same way every time. We always focus on one or another element, depending on the purpose of relating the experience, the audience, the brevity or detail involved, etc.
The lesson manual asks an intriguing question after referencing JS-H 1:6:
For, notwithstanding the great love which the converts to these different faiths expressed at the time of their conversion, and the great zeal manifested by the respective clergy, who were active in getting up and promoting this extraordinary scene of religious feeling, in order to have everybody converted, as they were pleased to call it, let them join what sect they pleased; yet when the converts began to file off, some to one party and some to another, it was seen that the seemingly good feelings of both the priests and the converts were more pretended than real; for a scene of great confusion and bad feeling ensued—priest contending against priest, and convert against convert; so that all their good feelings one for another, if they ever had any, were entirely lost in a strife of words and a contest about opinions.
(Joseph Smith—History 1:6)
The question from the manual:
How can we handle disagreements without becoming contentious like the people described in this verse?
The contention Joseph described was between and among religious people who shared basic beliefs in Christianity, but who insisted that others agree with their particular interpretations and opinions.
We see this type of contention among apologists in the Church today. They seem obsessed with trying to get everyone else to agree with them.
An alternative approach is to present a variety of views, perspectives, interpretations and opinions, and allow people to make informed decisions about what to believe. That's the approach I favor.
Jonathan Edwards wrote about this problem when addressing those engaged in apologetics:
By this means the devil scatters the flock of Christ, and sets 'em one against another, and that with great heat of spirit, under a notion of zeal for God; and religion by degrees, degenerates into vain jangling; and during the strife, Satan leads both parties far out of the right way, driving each to great extremes, one on the right hand, and the other on the left, according as he finds they are most inclined, or most easily moved and swayed, till the right path in the middle, is almost wholly neglected.