Around 435, Patrick was commissioned, perhaps by bishops in Gaul and perhaps by the Pope, to go to Ireland as a bishop and missionary. Four years earlier another bishop, Palladius, had gone to Ireland to preach, but he was no longer there (my sources disagree on whether he had died, or had become discouraged and left Ireland to preach in Scotland). Patrick made his headquarters at Armagh in the North, where he built a school, and had the protection of the local monarch. From this base he made extensive missionary journeys, with considerable success. To say that he single-handedly turned Ireland from a pagan to a Christian country is an exaggeration, but is not far from the truth.
Almost everything we know about him comes from his own writings, available in English in the ANCIENT CHRISTIAN WRITERS series. He has left us an autobiography (called the CONFESSIO), a LETTER TO COROTICUS in which he denounces the slave trade and rebukes the British chieftain Coroticus for taking part in it, and the LORICA (or "Breastplate" a poem of disputed authorship traditionally attributed to Patrick), a work that has been called "part prayer, part anthem, and part incantation." The LORICA is found in many hymnals, and it is a truly magnificent hymn, found today in many hymnals. The translation into English as given here is by Cecil Frances Alexander, whose husband was archbishop of Armagh, and thus the direct successor of Patrick. She published nearly 400 poems and hymns of her own, including the well-known "There is a green hill far away," "Once in royal David's city," "Jesus calls us; o'er the tumult," and "All things bright and beautiful, All creatures great and small." Incidentally, since a reader has asked about the reference to "purity of virgin souls," I will venture my opinion that it refers to the condition of someone who has just been baptized, and is considered to be newly born in Christ, with an utterly clean slate.
THE LORICA, OR, ST PATRICK'S BREASTPLATE I bind unto myself today the strong Name of the Trinity, by invocation of the same, the Three in One, and One in Three. I bind this day to me forever, by power of faith, Christ's Incarnation; his baptism in the Jordan river; his death on cross for my salvation; his bursting from the spiced tomb; his riding up he heavenly way; his coming at the day of doom: I bind unto myself today. I bind unto myself the power of the great love of cherubim; the sweet "Well done" in judgement hour; the service of the seraphim; confessors' faith, apostles' word, the patriarchs' prayers, the prophets' scrolls; all good deeds done unto the Lord, and purity of virgin souls. I bind unto myself today the virtues of the starlit heaven, the glorious sun's life-giving ray, the whiteness of the moon at even, the flashing of the lightning free, the whirling wind's tempestuous shocks, the stable earth, the deep salt sea, around the old eternal rocks. I bind unto myself today the power of God to hold and lead, his eye to watch, his might to stay, his ear to hearken to my need; the wisdom of my God to teach, his hand to guide, his shield to ward; the word of God to give me speech, his heavenly host to be my guard. Christ be with me, Christ within me, Christ behind me, Christ before me, Christ beside me, Christ to win me, Christ to comfort and restore me, Christ beneath me, Christ above me, Christ in quiet, Christ in danger, Christ in hearts of all that love me, Christ in mouth of friend and stranger. I bind unto myself the Name, the strong Name of the Trinity, by invocation of the same, the Three in One, and One in Three. Of whom all nature hath creation, eternal Father, Spirit, Word: praise to the Lord of my salvation, salvation is of Christ the Lord.An aspect of Patrick's thought that shows very clearly through his writings is his awareness of himself as an unlearned exile, a former slave and a fugitive, who has learned the hard way to put his sole trust in God.