Mormon concludes the arguments of his discourse by emphasizing charity as the love of Christ. Of course the need for this definitional statement is directly related to the way in which the Greek was translated by the KJV translators. Other English translations do use the word love here instead of Charity. Therefore, this specific sentence must be included as a clarification of the English text, not part of a translation of a plate text.
The reason that this love is so important is that it is the witness of the humility of our souls, and that is the foundation for our hope and faith. All of these traits move us closer to God, and therefore, in the last days it may be “well” with us.