Final answer:
The visitor most likely kissed the stone cross to fulfill a qualification for sainthood.
Step-by-step explanation:
The visitor to Skellig Michael who kissed its stone cross probably did so for the purpose of fulfilling a qualification for sainthood. In the Middle Ages, pilgrimage to holy sites, such as Skellig Michael, was seen as a way to get closer to God and seek forgiveness for sins. Kissing the stone cross could be considered a devotional act and a demonstration of faith.