Hank, I think he is referring to "the faith" as in the faith and practice handed down to the churches from Christ through the apostles. The ordained man must be sound in "the faith" or the essentials of New Testament faith and practice or the apostles doctrine.
Well, it seems to me you are simply expressing Deuteronomy 29:29 - the secret things belong to the Lord but those things revealed are for us to do.
I don't know brother as to faith not being a mystery both in the biblical Pauline definition of "a mystery" and the secular definition of "a mystery".
Pauline: Both Jews and Gentiles were to be included in the covenant promise to Abraham, Isaac and Jacob (Israel).
Or at least the glory of what that actually meant: that God Himself would become a man, suffer and die for our sins and not only pierce through the veil opening the holy place to everyone - not just the high priest but ALSO that He would break down the wall of partition (prefigured as a shadow in the design of the temple - the wall separating believing Gentiles and circumcised Jews).
Ephesians 2
12 That at that time ye were without Christ, being aliens from the commonwealth of Israel, and strangers from the covenants of promise, having no hope, and without God in the world:
13 But now in Christ Jesus ye who sometimes were far off are made nigh by the blood of Christ.
14 For he is our peace, who hath made both one, and hath broken down the middle wall of partition between us;
Secular meaning: Actually grace (the forerunner to faith) is the mystery part:
How could we be redeemed after the indictment "The day that thou eatest thereof thou shalt surely die".
Via the seed of the woman: The virgin birth - God becomes flesh - a total mystery to the world even at the Christmas season.
How can God become human(assuming He even exits)? - mystery.
How can He give us eternal life as we all must die? - mystery
How can a virgin conceive? - a mystery to the world.
Grace:God's solution to our fall in sin - Mystery after mystery.
Fine by me (and by all of us I'm sure).
HankD