3 “Beloved, while I was making every effort to write you about our common salvation, I felt the necessity to write to you appealing that you contend earnestly for the faith that was once for all time handed down to the saints. 4 For certain people have crept in unnoticed, those who were long beforehand marked out for this condemnation, ungodly persons who turn the grace of our God into indecent behavior and deny our only Master and Lord, Jesus Christ.”
Once for all: Jude wants his readers to fight for truth because it is the very message from God to the world. This Gospel of grace is what God has handed down to the saints for delivery to the world. Jude is concerned about the message of God’s grace being perverted and leading people to deception.
Deny our only Master: The false teachers encouraged a life of celebration of sin and also had some form of denial of Jesus’s identity. All false teachings, as defined by the Bible, deny some aspect of Jesus, and encourage godless behavior. In this context the godless behavior is abusing grace through sinful behavior. The false teachers were likely appealing to eternal security as a reason to sin all-the-more. Such teachings are often the result of having heard the truth about God’s grace in Christ. If God’s grace is truly free, then it can naturally be twisted to encourage sin. A legalistic Gospel would never yield false teachings.