The little book of Jude contains some powerful words against straying from the faith. If you are in danger of wavering - or of placidly condoning the backsliding of other believers - give Jude a listen to!
Jude "reminds" (vs. 5) his audience of fellow Christians about those who lost everything by falling into sin. This includes the chosen people rescued out of Egypt through the Passover under Moses. It includes fallen angels who suffered the loss of their place in heaven because of their disobedience. Even Sodom and Gomorrah come up for a mention as examples of the punishment of God's wrath on sin.
This is a dire warning to the Church of Jesus Christ! Jude, the brother of Jesus, is intent on helping Christians have a right view of adhering to the faith and falling back into sin. We are to keep ourselves from the fruitless ways of sin and instead build ourselves up in the faith (vs. 20).
A timeless message is encapsulated in this brief biblical book full of allusions to Old Testament and Apocryphal events. (Jude also ends with a great benediction that I have used many times in my ministry.)