Verses 50 and 51 need to be read as a set, because Jacob clearly intends them to be contrasting parallels.
Verse 50 introduces two themes, that of money which may purchase things (in the case of verse 50 , specifically the absence of physical money) and the things of God. The image is that of a transaction. where money purchases some desired good. Verse 50 specifically opens the anomaly of someone with no money buying that which is priceless.
Of course the message is that all have access to the benefits of the gospel. The image of the purchase however, is the specific theme which ties to verse 51.
Where verse 50 has the impecunious purchasing an item of great value verse 51 presumes that one already has wealth, but chooses to purchase things of no lasting value. This very specific contrast between the lack of money/possession-of-great-value and wealth/possessions-of-no-lasting-worth, provides even greater highlight to the beginning set of condemnations Jacob has already covered:
2 Ne. 9:28 O that cunning plan of the evil one! O the vainness, and the frailties, and the foolishness of men! When they are learned they think they are wise, and they hearken not unto the counsel of God, for they set it aside, supposing they know of themselves, wherefore, their wisdom is foolishness and it profiteth them not. And they shall perish.
2 Ne. 9:29 But to be learned is good if they hearken unto the counsels of God.
2 Ne. 9:30 But wo unto the rich, who are rich as to the things of the world. For because they are rich they despise the poor, and they persecute the meek, and their hearts are upon their treasures; wherefore, their treasure is their god. And behold, their treasure shall perish with them also.
In this context, Jacob has particularly condemned wealth as a means to spiritual gifts. His emphasis both in directly condemning the pursuit of wealth (to the exclusion of the principles of the gospel must be viewed as a very real problem to be addressed.
The picture emerging of Nephite culture some 40+ years after leaving Jerusalem (and therefore perhaps 30 since the division of the Lehites into Lamanite and Nephite is one of a Nephite culture so well adapted to their new environment that the were first wealthy, and secondly, able to purchase with that wealth a presumption of position contrary to the rule of God.
Where did this capability come from? From whom were they able to purchase goods? From whom did they earn the wisdom of men against whom they had been counseled?
No other conclusion save the presence of established people with established customs makes any sense. In the absence of this scenario of more people, we are left with significant economic and ideological differences among only fifty or so people, not all of whom would be adults.
In such a small society, it would make more sense for such a call to repentance to be made in private. With only 50 people, everyone would know to whom the sermon was addressed , thus adding personal embarrassment to the public call to repentance. Only a much larger audience supplies the needed generality and individual anonymity for such a speech to be socially effective.