Now to Him who is able to establish you according to my gospel and the preaching of Jesus Christ, according to the revelation of the mystery which has been kept secret for long ages past, Romans 16:25 NASB
Mystery – Did you know that there are technically no mysteries in the Hebrew Scriptures? “Wait a minute,” you’ll say. “What about all those secrets revealed? What about the prophecies come true? What about Paul’s own words?” Amazingly, the Greek word mysterion does not appear in sacred literature until the Hellenistic period in books like Tobit, Judith, Sirach and 2 Maccabees. Mysterion is a word from the Greek view of life, not from the Hebraic view. In Greek thinking, a mystery is often associated with a hidden religious formula, a bit of knowledge about the universe revealed only to the “enlightened” of the faith. The Greek mystery religions are filled with secrets for controlling destiny. But the Bible has nothing to do with this view of life. In fact, the only place where anything even close to this appears is in the Aramaic term raz in the book of Daniel. There this word means “a concealed intimation of divinely ordained future events whose disclosure and interpretation is reserved for God alone and for those inspired by His Spirit.” In the very few other uses of mysterion in the LXX outside the Hellenistic books, mysterion means nothing more than private conversation. In general, the Bible is not a book of secrets. God’s desire, plan and purpose are clearly revealed. No one has to first believe in order to understand (but they do have to first obey).
This fact leads to two crucial lessons. First, everyone can know the truth about God right where they are. God does not hide in the far reaches of space. He does not conceal His thoughts about life on this planet. He tells us as plainly as possible what He desires, what He has done and what the consequence of our actions will be. No one can offer the excuse “I wasn’t initiated into the faith” as a reason for disobedience. This is particularly important as a rebuttal to the theological camp claiming the total depravity of Man’s intellect as well as Man’s will. If my mind is fallen along with my choices, then I cannot know the truth until after God redeems me and, consequently, if God doesn’t redeem me, it is very difficult to imagine He can hold me accountable for not doing what I didn’t know. Since the Bible does not contain mysteries, there is no excuse.
Second, Paul’s Hebrew orientation leads us to conclude that he uses the Greek mysterion in the same sense as the Hebrew raz, not in the way it is used in the mystery religions. Paul thinks of mystery as something initiated and controlled entirely by God, revealed only to those whom God chooses to illumine. That’s what the word means in Daniel. But once we see this, we are confronted by an enormously important fact. Paul is not writing to the select few. He is writing to everyone who reads his letter. And that means that the secret is out. Anyone can know what God knows about this because everyone is included in the mysterion. Therefore, there is no longer any mystery. You and I can know, right now, what God wants us to know. God has pulled back the curtain and let all of us take a look. And that’s why knowing the mystery is so important because now we are all accountable. You and I no longer have the excuse, “Oh, God. I didn’t know.” Yes, we did. The only mystery left is what we are going to do about it.
Topical Index: mystery, mysterion, raz, secret, Romans 16:25
 G. Bornkamm, mysterion in TDNT, Vol 4., p. 815.