Actually JUDE "fought" religious people who told Paul that he was "preaching license to sin"... so, in Paul's day, it was called "sin so that Grace will come".
Its been updated, as a phase in the last 50 yrs.
JUDE teaches that religious legalists.........(people who are trying to go to heaven by works) or (believers who dont trust in Christ to keep them saved), created this concept that is now known as "OSAS".
See, when you believe you can lose your salvation, its because the person does not trust in Christ alone, to keep them saved.
So, in that case, what are they trusting to get them to heaven, if they dont BELIEVE that once you are saved, Christ always keeps you saved?
So, this person, is trying to keep themselves saved, and so, they will reject any teaching that trusts in Jesus The Christ Alone who keeps you eternally saved.
So, the OSAS, is what JUDE stated, are these people who are trying to save themselves, or keep themselves saved... who dont want any True Gospel that has JESUS keeping them saved, so they say that if you have real trust in Christ to keep you saved, you are teaching that Jesus is the Savior, who keeps you saved and they reject that as OSAS.
They redefined "Jesus is eternal Savior" as "OSAS"... or "license to sin".