I. After congratulating the Emperor on his noble conduct, he deprecates random inquiries into the tenets of the Faith.
Although I have replied already to your Grace by the hand of the Constantinopolitan clergy, yet on receiving your clemency's mercy through the illustrious prefect of the city, my son Tatian, I found still greater cause for congratulation, because I have learned your strong eagerness for the Church's peace. And this holy desire as in fairness it deserves, secures for your empire the same happy condition as you seek for religion. For when the Spirit of God establishes harmony among Christian princes, a twofold confidence is produced throughout the world, because the progress of love and faith makes the power of their arms in both directions unconquerable, so that God being propitiated by one confession, the falseness of heretics and the enmity of barbarians are simultaneously overthrown, most glorious Emperor.
The hope, therefore, of heavenly aid being increased through the Emperor's friendship, I venture with the greater confidence to appeal to your Grace on behalf of the mystery of man's salvation, not to allow any one in vain and presumptuous craftiness to inquire what must be held, as if it were uncertain. And although we may not in a single word dissent from the teaching of the Gospels and Apostles, nor entertain any opinion on the Divine Scriptures different to what the blessed Apostles and our Fathers learned and taught, now in these latter days unlearned and blasphemous inquiries are set on foot, which of old the Holy Spirit crushed by the disciples of the Truth, so soon as the devil aroused them in hearts which were suited to his purpose.
Source: Letters (New Advent)