He returned as a priest eager to spread the gospel message among a people who were still practicing human sacrifice and were the major slave traders of their day. Patrick found a way to plant the gospel in that culture, proving himself a missionary of great skill. He believed God had chosen him to convert the Irish. Drawing on his own struggles earlier in life, he preached in a way that had special meaning to a people who were downtrodden and commonly dismissed as barbarian.
St. Patrick found God in nature, in people, in the Church he loved and served. He is a saint for the Irish—and for all peoples.
You can read about St. Patrick in his own words in the Confession of St. Patrick
Here is an excerpt:
Whence I, once rustic, exiled, unlearned, who does not know how to provide for the future, this at least I know most certainly that before I was humiliated I was like a stone Lying in the deep mire; and He that is mighty came and in His mercy lifted me up, and raised me aloft, and placed me on the top of the wall. And therefore I ought to cry out aloud and so also render something to the Lord for His great benefits here and in eternity — benefits which the mind of men is unable to appraise.
Wherefore, then, be astonished, ye great and little that fear God, and you men of letters on your estates, listen and pore over this. Who was it that roused up me, the fool that I am, from the midst of those who in the eyes of men are wise, and expert in law, and powerful in word and in everything? And He inspired me — me, the outcast of this world — before others, to be the man (if only I could!) who, with fear and reverence and without blame, should faithfully serve the people to whom the love of Christ conveyed and gave me for the duration of my life, if I should be worthy; yes indeed, to serve them humbly and sincerely.