Reading the book of Jude with the question ‘is salvation from God once given never lost?’ what does this book say. Jude says that he is talking to the reader about the common salvation and the need to contend for the faith. He gives the example of how the children of Israel were saved by God and afterward were destroyed because they believed not. He gives the example of how angels who left their first place by their own volition are now reserved unto darkness and judgment. He talks about Sodom and Gomorrah who gave themselves over to fornication and the seeking of strange flesh who will suffer the vengeance of eternal fire.
If we look at these examples as instructive for us, they would seem to tell us that we need to keep ourselves from unbelief, self serving ambition, and sexual sins in order to avoid destruction and judgment. “Keep yourselves in the love of God, looking for the mercy of our Lord Jesus Christ unto eternal life” Jude says. This is an admonishment that we need to be diligent and not liaise-fair toward the faith of God delivered at one time to the saints. False teachers will come in walking after their own ungodly lusts and turn many to ungodly teaching and falsehoods.
Based on what Jude exhorts in this book I would say that once saved, always saved, is not an entirely correct teaching according to Bible scripture. We do need to walk with God and turn away from and deny our fleshly lusts in order to secure our salvation.