BT BQ 99a(20) :סוף סוף למאי יהבה ניהליה לרכוכיה כיון דרככיה הינו שבחיה‏ : in the final analysis, why did he give it to him? To soften it. When he softened it, that was its improvement
See the entire entry for rkk vb. to be soft