1 Inasmuch as many have undertaken to compile an account of the things accomplished among us, 2 just as they were handed down to us by those who from the beginning were eyewitnesses and servants of the word, 3 it seemed fitting for me as well, having investigated everything carefully from the beginning, to write it out for you in consecutive order, most excellent Theophilus; 4 so that you may know the exact truth about the things you have been taught. (Luke 1) [NASB]
The term κράτιστε is "used in addressing men of prominent rank or office." In his book, Paul on Trial, John H Mauck states:
"Most excellent," as a form of address, was used primarily as a title for rulers or governmental officials...1
This becomes a key point for his thesis Luke wrote what should be examined as a legal brief to a Roman official (a cognitionibus or possibly a rhetor) assigned to Paul's case. 2 Mauck's assumption is someone who is called "most excellent" must also be Roman.
The use in Acts supports understanding κράτιστε as a way Roman officials were addressed:
“Claudius Lysias, to the most excellent governor Felix, greetings. (23:26)
we acknowledge this in every way and everywhere, most excellent Felix, with all thankfulness. (24:3)
But Paul said, “I am not out of my mind, most excellent Festus, but I utter words of sober truth. (26:25)
Both Felix and Festus are addressed as κράτιστε. Claudius Lysias, Tertullus, and Paul all use the same term when addressing the governor (although Tertullus and Paul omit the position).
While the office of the High Priest was prescribed by Scripture, during the period covered by Luke-Acts, this office was filled/approved by Roman authority. In this sense the legal standing of the High Priest could be considered the same as the governor: they were appointed to the position.
Can Luke's use of κράτιστε be taken as his way of acknowledging someone who held the office of High Priest?
1. John W. Mauck, Paul on Trial, Thomas Nelson, 2001, p. vii
2. Ibid., p. 27