The author identifies himself as Jude, another form of the Hebrew name Judah. He was most likely Judas the brother of our Lord.
Although Jude was eager to write to his readers about salvation, he thought he ,use instead warn them about certain immoral men circulating among them who qwerty perverting the grace of God. Apparently these false teachers were trying to convince believers that being saved by grace gave them license to sin since their sins would no longer be held against them.
"See, The Lord is coming with thousands of his holy ones to judge everyone, and to convict all the ungodly acts they have done in the ungodly in the ungodly way, and of all the harsh words ungodly sinners have spoken against him." (14-15)
"In the last times there will be scoffers who will follow their own ungodly desires." These are the men who divide you, who follow mere natural instincts and who do not have the Spirit. But you, dear friends, build yourselves up in your most holy faith and pray in the Holy Spirit. Keep yourselves in God's love as you wait for the mercy of our Lord Jesus Christ to bring you to eternal life. (18-21)