The book of Jude was written, most likely by another half brother of Jesus (the other one being James). It was written about A.D. 65.
It is a short, one chapter writing originally penned to extol God's salvation in Jesus Christ (1:3). However, he found it necessary to change his plans and exhort and warn the church about false teachings that some were bringing into the church. Jude doesn't spare any words as he warns the church to be careful of error. He lays it on the line!
The chapter ends with a very positive benediction (1:24-25) bringing praise to God who is able to keep his people from falling.