For from his fullness we have all received, grace upon grace.
Eventually every well no matter how popular or how useful will run dry. To those people who depend on the the well it can be devastating once it no longer yields water. A dry well can cause people to travel miles for the life sustaining substance.
This is a stark contrast to the well of grace provided to humanity once Christ was born. We have received grace in place of grace, one blessing after another. Where one supply of grace is exhausted another is available, resulting in an unending flow of undeserved favor in the sight of God.