"Dear friends," Jude says, "I felt I had to write and urge you to contend for the faith that was once for all entrusted to the saints." (Jude vs 3) A challenge to the faith had arisen, so Jude writes to "urge" them – that is, to motivate and plead with them – "to contend for the faith". Not only is the faith to be proclaimed, it is to be defended from corruption.
Paul reserved stern words for those who proclaim a message contrary to the apostolic gospel: "But even if we or an angel from heaven should preach a gospel other than the one we preached to you, let him be eternally condemned. As we have already said, so now I say again: If anybody is preaching to you a gospel other than what you accepted, let him be eternally condemned." (Galatians 1:8-9) And those who were proclaiming a different gospel were confronted by Paul. He recalls how, "We did not give into to them for a moment, so that the truth of the gospel might remain with you." (Galatians 2:5) That's contending for "the faith".
The Faith, the Gospel and the Cross
"The faith" is not our personal faith, our trust in Jesus to save us, but the message as to how Jesus saves us – through his death and resurrection. That's "the faith" to which Jude refers. This becomes clear when we tie several scriptures together. In his letter to the Galatian believers, Paul gives an overall view of his ministry. He speaks about (1) "the gospel I preached", (2) "that I might preach him [Jesus] among the Gentiles", and (3) refers to "preaching the faith." (Galatians 1:11,16,23) Paul was not preaching three messages: the gospel, Jesus and the faith. No. Preaching the gospel is proclaiming what God has done for sinners through the Lord Jesus Christ; it is the same as telling sinners about Jesus. It is proclaiming the faith. These three expressions speak of one and the same subject.
The gospel Paul preached was all about the cross of Christ. Let's compare scripture with scripture. He says that the gospel "is the power of God unto salvation..." and that "the message of the cross... is the power of God" to those who are being saved. (Romans 1:16; 1 Corinthians 1:18) The gospel and the message of the cross are the same and display the power of God to save sinners. We must emphasise that there is no good news for sinners apart from the cross of Christ. When Scripture tells us that "Jesus was preached" we know that the message of how he saves sinners through his death was being proclaimed. For example, when Philip the evangelist went to Samaria he "proclaimed the Christ there... he preached the good news... [many] were baptised, both men and women." (Acts 8:5-12) And when he met the Ethiopian, he "told him the good news about Jesus" and the Ethiopian believed and was baptised. (Acts 8:35-38) What Philip was doing was preaching the gospel, telling him the message of the cross of Christ, proclaiming "the faith" to him. And when the gospel was being spread throughout Jerusalem, Luke tells us that "a large number of priests became obedient to the faith". (Acts 6:7) Being "obedient to the faith" is to believe the gospel. And the response of the priests to "the faith" was the same as that of the Ethiopian and the Samaritans.
Unrepeatable
"The faith" Jude tells us was "once for all entrusted to the saints". The word "once" is the same word used in Hebrews 10:10 where the sacrificial death of Jesus is said to have occurred "once for all". The word "once" means, "once, to be of perpetual validity, never needing repetition". What Jesus accomplished in his atoning death satisfied in full the holy justice of God and secured for us the full pardon of our sin; therefore it cannot ever be repeated. This is what the Bible calls "the faith". And it has been entrusted to the saints, in every generation, to contend for.
