A little while back I went to a rosary devotion and prayed with a bunch of people. When it was over, one of them explained to me that it was a real good idea to attend group rosaries, because, if you pray the rosary with a number of people, each gets "credit" for having prayed that number of rosaries.
At one level I appreciate the thought. On another I don't. I like it because it suggests the superabundance of grace. According to this model, the grace or "credit" of having prayed a rosary increases geometrically. That is to say, when one person prays the rosary, one portion of grace is received. If two people, then four, as each would receive two. If five people prayed the rosary together, then there would be 25 portions of grace. If 100, then 10,000, and so on.
Grace is always given utterly out of proportion with our desire, effort or willingness to receive it, so in this sense I like my friend's idea.
On the other hand, God does not dispense credit to those who do the things that God allegedly wants. As Jesus himself said, God lets the sun shine and the rain fall for both the just and unjust, because God loves his enemies just as much as his friends. Thus there is no sense in which one person has more "credit" than another before God. As Paul says over and over, all have sinned and fallen short of God's glory.
Even more, grace is not a quantifiable commodity like money, or a credit rating, the respect of a community, or human trust. Good or bad, saint or sinner (or miserable and unglamorous mix of both, as most of us are), we all move and have our being in the grace of God. It's like living and working in the light of day. Most of the time we are just looking at stuff and tasks, without reflecting on the Light that illuminates our vision and understanding in the first place.