Erosion? No. In fact this grooving into the wall of Alrewas Church is another example of a habit of medievel times - that of sharpening your arrow-heads using the friable stone of a church building.
Men were required by law to practise their archery skills regularly, and would meet by the church to do it. So why not use the church wall as a form of whet-stone at the same time?!
There's another example at Checkley.