For the truth, to the support and establishment of which every Christian by his behaviour in the Church is bound to contribute, is indisputably something great and profound. By the admission of all, the mystery of the Christian faith is a deep and weighty one; and the responsibility of helping or hindering its establishment is proportionately deep and weighty. Other things may be matter of dispute, but this not. "Without controversy great is the mystery of godliness."
Why does St. Paul speak of the Truth as "the mystery of godliness"? In order to express both the Divine and the human aspects of the Christian faith. On the Divine side the Gospel is a mystery, a disclosed secret. It is a body of truth originally hidden from man's knowledge, to which man by his own unaided reason and abilities would never be able to find the way. In one word it is a revelation: a communication by God to men of Truth which they could not have discovered for themselves. "Mystery" is one of those words which Christianity has borrowed from paganism, but has consecrated to new uses by gloriously transfiguring its meaning. The heathen mystery was something always kept hidden from the bulk of mankind; a secret to which only a privileged few were admitted. It encouraged, in the very centre of religion itself, selfishness and exclusiveness. The Christian mystery, on the other hand, is something once hidden, but now made known, not to a select few, but to all. The term, therefore, involves a splendid paradox: it is a secret revealed to every one. In St. Paul's own words to the Romans (xvi. 25), "the revelation of the mystery which hath been kept in silence through times eternal, but now is manifested, and by the scriptures of the prophets, according to the commandment of the eternal God, is made known unto all the nations." He rarely uses the word mystery without combining with it some other word signifying to reveal, manifest, or make known.[53]
But the Christian faith is not only a mystery but a "mystery of godliness." It not only tells of the bounty of Almighty God in revealing His eternal counsels to man, but it also tells of man's obligations in consequence of being initiated. It is a mystery, not "of lawlessness" (2 Thess. ii. 7), but "of godliness." Those who accept it "profess godliness"; profess reverence to the God who has made it known to them. It teaches plainly on what principle we are to regulate "how men ought to behave themselves in the household of God." The Gospel is a mystery of piety, a mystery of reverence and of religious life. Holy itself, and proceeding from the Holy One, it bids its recipients be holy, even as He is Holy Who gives it.