Much that is popularly believed about Patrick is simply fiction and fantasy.
Patrick is known primarily from his two short works, his epistle and his confession, and we can piece together from them an outline of his life. Beyond that there are some strong traditions, such as the association with Slemish. However the medieval lives of Patrick are largely spurious and propagandist, filled with distortion, exaggeration and invention.
Patrick was the son of a British churchman and grew up in a Christian home on the west coast of Britain, probably in south-west Scotland or the north-west of England.
When he was sixteen years of age he was captured by raiders who sold him into slavery and he spent six years as a slave in Ulster, looking after animals on the slopes of Slemish mountain in county Antrim. There he remembered what he had been taught as a young boy and he was convicted of his sin and converted to Christ. Later he excaped and made his way back to his home and family.
Some years after this, he heard the call to come across to the island of Ireland and preach the gospel. He landed in Strangford Lough and after the conversion of a local chieftain he established his first church at Saul. His ministry lasted about forty years and covered the length and breadth of Ulster. Through his preaching many people turned from their pagan faith and became Christians. Churches were built and men of god were ordained to minister in these churches. This was God's work, done in God's way and thereby Patrick secured the permanence of his work in Ulster.
According to the historian Dr Jonathan Bardon: 'Most places traditionally associated with Patrick ... are in the northern half of Ireland and it was probably in Ulster that he did most of his work.' This is also the view of Professor Hugh Kearney: 'The likelihood is that he confined himself to the kingdom of the Ulaid (Ilster) with it capital at Emain Macha (Armagh).'
In trying to ascertain the teaching of Patrick, we must go to his own writings as the direct and supreme source of information. From that source we find that the message that Patrick preached in ulster was a biblical, evangelical and Trinitarian message. It was the same message that the Apsotles had preached four centuries earlier, it was the message which the Reformers preached a thousand years later and it is the message which evangelical Protestants preach today - We are saved by grace, through faith, in Christ. Patrick had a profound knowledge and understanding of the Bible and his writings are full of quotations from Holy Scripture.
Finally, turning to the myths about Patrick:
1. Patrick was sent to Ireland by Pope Celestine I - there is no evidence to link Patrick with Rome. His mission was sanctioned by God, not by Rome and the ancient church in the British Isles was independent of Rome.
2. Patrick was canonised by the Roman Catholic Church - Patrick was never canonised by Rome but he was a saint in the true Biblical sense for he was a true Christian.
3. Patrick wore a mitre and vestments - this is the usual depiction of Patrick but it is an anachronism. The mitre and vestments were not introduced until centuries after the time of Patrick and the first printed depiction of him in this way appeared in 1624. This was an attempt by the Roman Catholic Church to claim Patrick for themselves.
4. Patrick used the shamrock to explain the Trinity - this story did not appear in print until 1727. At about the same time the shamrock seems to have acquired its use as an emblem of Ireland. This is a myth created about a thousand years after his death.
5. Patrick drove the snakes out of Ireland into the sea - ancient writers confirm that there never were snakes in Ireland.
6. Patrick performed many marvels and wonders - these spurious stories were invented by the authors of the medieval lives of Patrick.
7. Patrick converted the High King of Ireland - there wasn't a High King of Ireland in the time of Patrick.
Patrick was brought as a slave to Ulster, was converted in Ulster, returned to Ulster, ministered in Ulster, died in Ulster and was buried in Ulster soil - Patrick was God's man for Ulster, the Apostle of Ulster.