Non-Christian Adepts?

In the New Testament, St. Paul teaches that God is evident through the work of His creation. Everyone, everywhere, is aware of God (they just don't know Him by that moniker). Therefore, everyone has the potential to experience a metaphysical encounter with The Almighty and be transformed into an Adept. Even the most abrasive, foul-mouthed of the lot.
However, Christianity is not a man-made religion, it is God's work. The fact that the Established Orders are predominately populated by Xtrians is proof enough of that for many. Further proof of this is that the Order of Judges is completely manned by Christians, and it falls to the Judges to ensure the salvation of their fellow Adepts.