The faith (with definite article) refers to the body of Christian doctrine, not personal belief.

Mike distinguishes personal faith (trust in Christ) from the faith (the definite article signals doctrinal content). He cites 1 Timothy 6:21 (swerving from the faith = adopting false doctrines) and Jude 3 (contend for the faith once for all delivered to the saints). The implication: Christian doctrine was fully delivered by the end of the first century, making the church inherently resistant to new theology — we always return to the apostolic deposit.