There are no changes from Matthew 6:19–21.
The underlying theme of everything Jesus has taught has been the relationship of the individual to God. In the Beatitudes, it underscored the ultimate goal that transcends many of the hardships of this life.
The series of amplifications taught how the law of Moses was fulfilled, not by removing the moral laws, but by expanding them.
Most recently, the theme was how the individual approached deity.
These verses provide the reason behind all of the actions that have been described up to this point. Acting in the ways Jesus has described will “lay up … treasures in heaven.” That word choice was intentional; Jesus’s audiences on both hemispheres were well aware of what earthly treasures were like. What they are taught is that by acting correctly and living the commandments, they prepare themselves for greater treasures in the kingdom of heaven.
The declaration that “where your treasure is, there will your heart be also” is particularly poignant for the Nephites. Their history is replete with times when they set their hearts on worldly riches, and it led them away from God’s commandments, and therefore away from the protection of the covenant of the land. That led to destruction.