The question of affirming or not affirming the Trinity can be the subject of theological debate. However, the truly serious error — and what crosses into heresy — is to deny that a person who sincerely believes and follows the teachings of Christ and His apostles can be saved without making a formal Trinitarian confession. Such a denial falls under the strong warning in Galatians 1, where Paul declares a curse on anyone who proclaims a gospel contrary to the one originally preached.
A deeply troubling situation arises when churches will not receive such believers unless they adopt specific Trinitarian terminology. This imposes a barrier where Scripture has not placed one, creating confusion and acting as a stumbling block to the believer’s full inclusion in the body of Christ.
Such exclusion not only distorts the nature of the gospel but also underscores the relevance and severity of Paul’s warning in Galatians 1.