Jude, the brother of Jesus, longed to write to his beloved brethren in Christ about their "common salvation." The Holy Spirit prompted him to write about something else. Out of necessity he wrote to them an exhortation: Contend earnestly for the faith!
Some had "crept in unnoticed" and "the faith which was once for all delivered to the saints" was at stake. Those "called, sanctified by God the Father, and preserved in Jesus Christ" are exhorted to contend earnestly for the body of truth that had been delivered to them by the Holy Spirit. The faith must be defended by God's saints!
There is truth and error. There is right and wrong. Contend earnestly for the faith that reveals truth and righteousness!
Jason Cicero