Charity does not grow by addition, like a heap of wheat. This addition would multiply charity without making it more intense. The increase would be in the order of quantity rather than quality, which is quite a different thing. In reality, charity or love increases in us in so far as it becomes stronger, takes deeper root in our will. As with the scholar, learning becomes more profound, more penetrating, more certain, without always reaching out to new conclusions. So charity grows in us by making us love God more perfectly and more purely for himself, and our neighbour for God.
Fr. Reginald Garrigou-Lagrange, O.P. The Three Ages of the Interior Life: Prelude of Eternal Life Volume One. Translation by Sister M. Timothy Doyle, Tan Books and Publishers INC, 1989, pp 132-133
Ran across this quote in an article from Homiletic and Pastoral Review.