While St. Patrick successfully brought Christianity to Ireland, it was up to successive generations to ensure it did not die out. One of the most influential saints who helped foster Christianity in the country was St. Finnian of Clonard.
He was born around 470 and was instructed in the faith by the disciples of St. Patrick. Some traditions say that Finnian studied in Gaul where St. Martin of Tours established a monastic center. Eventually he made his way back to Ireland and founded an influential monastery at Clonard. It was for his work there that Finnian would later be called "tutor of saints."
A great number of monks came to him for instruction and it is said that there were over 3,000 pupils at Clonard at any given time. Whatever the number may be, under his tutelage there grew a new generation of monastic saints.
In particular, Irish writers over the centuries signaled out "12 Apostles of Erin" who studied under Finnian and further ingrained Christianity into Irish culture.
St. Ciaran of Saighir (Seir-Kieran)
St. Ciaran of Clonmacnois
St. Brendan of Birr
St. Brendan of Clonfert
St. Columba of Tir-da-glasí
St. Columba of Iona
St. Mobhí of Glasnevin
St. Ruadhan of Lorrha
St. Senan of Iniscathay
St. Ninnidh the Saintly of Loch Erne
St. Lasserian mac Nadfraech
St. Canice of Aghaboe
The list can vary according to the writer, and there exist many other saints whose faith was fostered at the great school of Clonard.
Suffice to say it illustrates the reality that sometimes all that is needed is one individual to say "yes" to God for many others to follow in line.