When harvesting crops, forgotten fruits are meant to be left for the poor and needy rather than carefully recovered. The property is the Lord’s, and the Israelites are mere stewards of that property.
If a man dies without bearing a son, his brother is meant to marry the widow and bear a son for him. This is not only so that the man’s heritage is preserved, but also so that the widow may be cared for by these sons. The younger brother does not profit from this arrangment, but serves his duty to their family and averts selfishness.
Finally, the firstfruits of crops are offered to the Lord and to the poor. All of this is written to remind us to constantly consider the Lord and the poor when we have abundance. Moreover we are called not to follow the minimum requirements, but extend them as FAR as our heart and soul can bear!