Dear FRiend, I already answered this question of yours.
Paul warned them because they could fall into paganism themselves.
.. and lead others into paganism.
And abandoning Christ and taking up paganism can entrap a Christian.
Nor does Paul ever say so when if it were true, this was a great place to say so.
It cannot harm their salvation. That is decided.
The BEMA Seat Judgment is real. It happens In Heaven for ALL those in the Body of Christ Believers. The way GOD brings fallen men and women into New Birth is through those He has birthed from above. They are converted by the witness of those He has converted, their lives. He is not using your Catholic rituals or rites or priestly utterances or incantations. He works on their spirit which is captured in their behavior mechanism. The behavior mechanism 'compares and contrasts'. Paul is warning the new converts to conform their behavior to a level which witnesses to those not yet converted. He is not warning so the new borns from above will not lose or forfeit their newborn status and be damned. That is a hard thing for a Cathoolic to grasp, being that that religion is a works based religion Christianity lookalike.