This letter was written as a warning against leaders who were teaching things about God that weren't true. People had waited for years for the Messiah to come, but now they were becoming impatient and starting to change their beliefs. This false teaching crept in almost unnoticed, and Jude wanted to put people straight.
This letter is a great encouragement to pray about, and check with the Bible, the things we assume about God. We should not shape our view of God based solely on what we experience, the things we go through, or what other people tell us. Instead we should be checking with the Bible. Jude ends with a brilliant prayer for all Christians.