Okay. Patrick of Ireland did not write a treatise on religious liberty. Or specifically mention it in his writings. But it is St. Patrick’s Day. And what I have below is a quote from Patrick of Ireland (from two different translations). In his letter to the soldiers of Coroticus Patrick asserted that Christians should be able to exist and worship free of molestation, appealed not to authorities but directly to the guilty parties, and showed that those who had molested Christians were guilty before God and that God, not Patrick, would take care of it.
“That is why I will cry aloud with sadness and grief: O my fairest and most loving brothers and sisters whom I begot without number in Christ, what am I to do for you? I am not worthy to come to the aid either of God or of human beings. The evil of evil people has prevailed over us. We have been made as if we were complete outsiders. Can it be they do not believe that we have received one and the same Baptism, or that we have one and the same God as father. For them, it is a disgrace that we are from Ireland. Remember what Scripture says: ‘Do you not have the one God? Then why have you each abandoned your neighbour?’”
From Letter to the Soldiers of Coroticus © 2011 Royal Irish Academy
“Because of all this, my voice is raised in sorrow and mourning. Oh, my most beautiful, my lovely brethren and my sons ‘whom I begot in Christ,’ I have lost count of your number, what can I do to help you now? I am not worthy to come to the help of God or men. ‘We have been overwhelmed by the wickedness of unjust men,’ it is as if ‘we had been made outsiders.’ They find it unacceptable that we are Irish. But it says ‘Is it not true that you all have but one God? Why then have you, each one of you, abandoned your own neighbor?’”
From Letter to the Soldiers of Coroticus, translated by John Skinner in his book The Confession of St. Patrick