"Saving" faith is being convinced of the claims of Scripture concerning the redemptive work and person of Jesus. Faith is not the foundation of salvation it believes in the foundation of salvation.
Scripture reveals Christ's person, His deity, His humanity, His redemptive propitiation for His people, His promises, and much more. Most of all, Scripture speaks to the sufficiency and efficacy of Christ's work.
When a person is saved by God, that person is granted the gift of believing in the simple nature of these revelations on their own behalf. They then grow, learn, and are encouraged by right teaching as they begin to understand more and more of what Scripture reveals.
Sadly, many sheep can be led astray for a season, but God is faithful and they will not be deceived. His sheep will hear His voice and they will follow after Him. Let's be sure we're speaking the language of Jesus, not the language of men.
Imagine the believers of Galatia who entertained the addition of circumcision when Paul had already taught them the truth. That correction was doubly painful.
Be at peace beloved. God's word will not fail and you will not be lost. Make certain you listen to the Scripture on your own so you can discern the WHOLE COUNSEL of God's word. And be sure to judge rightly those who love you, not those who Lord over you with harsh doctrine and a lack of patience.
Be a Berean, not a ditto head.