Odd stones

There are similar markings at the entrance to Aghowle Church in county Wicklow and possibly Fore (and a few other Early Christian sites that I can't recall just now).

These markings are often thought to be the result of sharpening a metal edge. That's problematic and may have been discussed here previously.
If the markings are the result of drawing a metal edge along the stone, then repeatedly doing so would result not only in a deepening of the groove but also in a dulling of the edge. It is highly unlikely that an edge or blade would be sharpened by drawing it through these grooves.

Might drawing an edge through a groove in stone have been a symbolic act to demonstrate an interest in peace rather than violence? Could armed churchgoers have symbolically 'blunted' their weapons before entering the church?

A more mundane explanation might be that the grooves are the result of initial shaping of a blade at an early stage in the manufacturing process. That possibility could be supported by the not infrequent association of evidence for ironworking with Early christian sites.