John, 

The Communion of Saints involves a whole plane of supernatural action - how grace and sin fully operate in the world. 

A prayer or fast you offered 40 years ago in Vietnam may be still having a supernatural effect in Puerto Rick today.    If we doubt, then Jesus will be unable - as  the readings of the Mass told us recently -  to perform His work in us and in the world.  He will have to find another way to help us. 

We have to have more faith (and humility) that we don't know the means that God uses to help us.    We cannot live with mere human vision.  That's what faith is about. 

So my un-generosity tomorrow can have repercussions widely among the children of God..and my prayer and "beginning again" can as well.