ISB ~ Jude 1 v4

admission … secretly gained:The false teachers were intruders who smuggled their errors into unsuspecting communities.

designated:Literally, “written beforehand”. Jude evokes the biblical image of heavenly books filled with the names and deeds of both saints and sinners (Ex 32:32; Ps 69:28; Phil 4:3; Rev 20:12).

pervert the grace:The intruders misinterpret “freedom in Christ” as a license to do evil (8, 10, 16). The problem of shirking the moral responsibilities of the gospel, often called antinomianism, was the target of several apostolic warnings (Rom 6:15; Gal 5:13; 1 Pet 2:16). Perhaps the perpetrators radically distorted Paul’s teaching on Christian freedom, or possibly they embraced proto-Gnostic ideas that sanctioned immoral behavior on the basis of a theoretical separation between matter (the body) and spirit (the soul).

deny our only Master:They either denied the Lordship of Christ by their shameful behavior (Tit 1:16) or promoted a defective understanding of who Christ really is (1 Jn 2:22).