“…the preaching of Jesus Christ, according to the revelation of the mystery, which was kept secret since the world began…” – Rom 16:25
This should be clear enough, but it is often rejected by claiming that the mystery of Christ was prophesied but hidden in the old testament, the law, or the promises given to Abraham.
This is an outright denial of what Paul says by inspiration that the mystery of Christ was “kept secret since the world began”.
If something was revealed since the world began until Paul, it can not be the mystery of Christ revealed to Paul.
“Even the mystery which hath been hid from ages and from generations, but now is made manifest to his saints” – Col 1:26
The mystery was hidden from past ages of time. There is no time in the past in which this mystery was made known, until now.
“But Peter says the prophets prophesied of grace in 1 Pet 1:10”
Then what was prophesied about grace can not be the mystery of Christ, even if they did not understand what they prophesied.
That they prophesied at all means God revealed and did not keep it secret (Deu 29:29).
God’s word says the mystery was hid “from generations”. There is no generation of men that was given this information until Paul.
“Then, where was the mystery of Christ hid if not in the Old Testament writings?”
Eph 3:9 explains that the mystery was “from the beginning of the world hid in God, who created all things by Jesus Christ”.
God the creator, before the world began, decided to keep this mystery a secret, hidden, and unknown until He revealed it to the apostle Paul by the Spirit (Eph 3:3-5; Gal 1:15-16; Rom 15:15-16).
It was not hidden in the Old Testament writings, nor in the New Testament writings, nor in the promises given to Abraham.
“But the prophets did speak of Christ’s death, forgiveness of sins, and grace to Gentiles.”
Then those things cannot be the mystery kept secret, unknown to ages and generations, hidden from the beginning in God as the Scripture states.
If the mystery was in prophecy then it ceases to be a mystery.
This is the foundation of rightly dividing the word of truth, and the only way to keep from denying the secret nature of the mystery.
To Paul was revealed the mystery of Christ’s headship in heaven with one body called the church united to him freely by God’s grace through Christ’s death, blood, and resurrection.
This mystery of Christ is not found at all in prophecy.
If something was revealed since the world began until Paul, it can not be the mystery of Christ revealed first to Paul.
“This is a great mystery: but I speak concerning Christ and the church.” – Eph 5:32