The mystery of faith is a term that occurs in 1 Timothy 3:9. Depending on the English translation, the Greek phrase τὸ μυστήριον τῆς πίστεως is translated “the mystery of faith,” “the mystery of the faith,” or “the deep truths of the faith.”
The verse in which the phrase appears is about deacons. Paul is advising Timothy about what sort of man should be trusted with the office of deacon in order to serve the local church body. Paul says a deacon should be dignified, truthful, and one who “holds to the mystery of faith with a clear conscience” (1 Timothy 3:9). In this context, Paul is simply saying that the man who serves the church should be a believer who is mature, who has a firm grasp on the basic elements of the gospel, and whose life matches his profession of faith.
A “mystery” in the New Testament is something that had at one time been hidden but is now revealed to God’s people. Jesus told His disciples, “To you it has been granted to know the mysteries of the kingdom of heaven, but to them it has not been granted” (Matthew 13:11, NASB). The apostle Paul often spoke of such “mysteries”: Jesus’ incarnation (1 Timothy 3:16), the indwelling of the Spirit (Colossians 1:26–27), the unity of the church (Ephesians 3:4–6), the rapture (1 Corinthians 15:51–52), and the gospel itself (Colossians 4:3). All these truths were “hidden” from the prophets of old but have been revealed plainly to us today. They are “mysteries” that are no longer mysterious to the child of God. “The mystery of faith” is the divinely revealed truth about grace, redemption, and forgiveness in Christ.
The message of Christ’s sacrifice for sin and His resurrection (the message that Paul refers to as “the faith”) is easy to understand. The basic gospel message is simple enough for even the youngest believer, but it is also a humbling mystery that was only hinted at throughout the time of the Old Covenant. Now God’s plan of salvation has been revealed in His Son, Jesus Christ, and we are held responsible to “hold” that message firmly.
When Paul advises Timothy to appoint deacons who “hold to the mystery of the faith with a clear conscience,” he is telling Timothy to find mature believers—men who understand the message of the gospel and are living it out. “Oh, the depth of the riches of the wisdom and knowledge of God!” (Romans 11:33). Oh, the condescension of Christ who has made manifest the mysteries of heaven to us!