Scofield Reference Notes (1917 Edition)Chapter 16
16:25 Now to him that is of power to stablish you according to my gospel, and the preaching of Jesus Christ, according to the revelation of the mystery, which was kept secret since the world began,
16:26 But now is made manifest, and by the scriptures of the prophets, according to the commandment of the everlasting God, made known to all nations for the obedience of faith:
(See Scofield "Matthew 13:11") . The "mystery" here is the Church; Ephesians 3:1-9.
See margin ref., (See Scofield "Romans 1:5") . Faith as a system, in contrast with law as a system.