Thesis: By and large, the New Testament speaks about the mystery of God as revealed in Jesus Christ. Below are the numerous examples of mystery (Greek: mysterion) in the context of speaking about revelation.
And Jesus said to them, "To you has been given the secret of the kingdom of God, but for those outside, everything comes in parables" (Mark 4:11; par. Matt. 13:11, Luke 8:10)
Now to God who is able to strengthen you according to my gospel and the proclamation of Jesus Christ, according to the revelation of the mystery that was kept secret for long ages but is now disclosed, and through the prophetic writings is made known to all the Gentiles, according to the command of the eternal God, to bring about the obedience of faith -- to the only wise God, through Jesus Christ, to whom be the glory forever! Amen. (Romans 16:25-27)
When I came to you, brothers and sisters, I did not come proclaiming the mystery of God to you in lofty words or wisdom. 2 For I decided to know nothing among you except Jesus Christ, and him crucified. 3 And I came to you in weakness and in fear and in much trembling. 4 My speech and my proclamation were not with plausible words of wisdom, but with a demonstration of the Spirit and of power, 5 so that your faith might rest not on human wisdom but on the power of God. 6 Yet among the mature we do speak wisdom, though it is not a wisdom of this age or of the rulers of this age, who are doomed to perish. 7 But we speak God's wisdom, secret and hidden [lit., "a mystery kept secret"], which God decreed before the ages for our glory. 8 None of the rulers of this age understood this; for if they had, they would not have crucified the Lord of glory. 9 But, as it is written, "What no eye has seen, nor ear heard, nor the human heart conceived, what God has prepared for those who love him"-- 10 these things God has revealed to us through the Spirit; for the Spirit searches everything, even the depths of God. (1 Corinthians 2:1-10)
Think of us in this way, as servants of Christ and stewards of God's mysteries. (1 Corinthians 4:1)
With all wisdom and insight 9 he has made known to us the mystery of his will, according to his good pleasure that he set forth in Christ, 10 as a plan for the fullness of time, to gather up all things in him, things in heaven and things on earth. (Ephesians 1:8b-10)
This is the reason that I Paul am a prisoner for Christ Jesus for the sake of you Gentiles-- 2 for surely you have already heard of the commission of God's grace that was given me for you, 3 and how the mystery was made known to me by revelation, as I wrote above in a few words, 4 a reading of which will enable you to perceive my understanding of the mystery of Christ. 5 In former generations this mystery was not made known to humankind, as it has now been revealed to his holy apostles and prophets by the Spirit: 6 that is, the Gentiles have become fellow heirs, members of the same body, and sharers in the promise in Christ Jesus through the gospel. 7 Of this gospel I have become a servant according to the gift of God's grace that was given me by the working of his power. 8 Although I am the very least of all the saints, this grace was given to me to bring to the Gentiles the news of the boundless riches of Christ, 9 and to make everyone see what is the plan of the mystery hidden for ages in God who created all things; 10 so that through the church the wisdom of God in its rich variety might now be made known to the rulers and authorities in the heavenly places. (Ephesians 3:1-10)
I became its servant according to God's commission that was given to me for you, to make the word of God fully known, 26 the mystery that has been hidden throughout the ages and generations but has now been revealed to his saints. 27 To them God chose to make known how great among the Gentiles are the riches of the glory of this mystery, which is Christ in you, the hope of glory. (Colossians 1:25-27)
I want their hearts to be encouraged and united in love, so that they
may have all the riches of assured understanding and have the knowledge
of God's mystery, that is, Christ himself, 3 in whom are hidden
all the treasures of wisdom and knowledge. (Colossians 2:2-3)
Anti-thesis: Pagan religion relies on the mystery of the gods in order to keep hidden our human responsibility for violence. How much has Christian religion slipped back into these mysteries? Did the slippage even begin to manifest itself in the late New Testament? Different are the references to mystery in the pastoral epistle, 1 Timothy, where the mystery of faith seems to be an accepted fact, with no talk of revelation:
1 Timothy 3:9 they must hold fast to the mystery of the faith with a clear conscience.
Or the revelation of the incarnation manifests "the mystery of our religion":
1 Timothy 3:16 Without any doubt, the mystery of our religion is great: He was revealed in flesh, vindicated in spirit, seen by angels, proclaimed among Gentiles, believed in throughout the world, taken up in glory.