christiani - were members of Christ's band of conspirators.
In Greek phonetics,the word chrestos (good) was, and is, pronounced christos. The conspiracy of the Christos is a conspiracy of those who are chrestos, a conspiracy of goodness.
For a complete analysis from then Cardinal Joseph Ratzinger, see "The Essential Pope Benedict XVI", edited by John F. Thornton and Susan B. Varenne and published by HarperSanFrancisco, 2007. The content is full of the Holy Father's speeches and important Homilies before he became Pope.