Why did Jude write about contending for the faith instead of about the common salvation?
Jude originally intended to write concerning the common salvation, the plan of salvation, but the Holy Spirit forbade him. Instead, it was needful for him to exhort believers to earnestly contend for the faith once delivered to the saints, because certain men had crept in unawares.
Les explains that Jude had evidently intended to write just a little letter concerning the plan of salvation, but the Holy Spirit forbade him to do that. Instead, Jude said it was needful to write and exhort believers to earnestly contend for the faith, the one and only faith once delivered to the saints. Les notes that this does not mean being obnoxious or taking people by the neck and shoving it down their throat, but it does mean taking a stand on what we believe and helping people see the truth of the Word of God. Jude then gives the reason in verse 4: certain men had crept in unawares, so nobody knows what they are up to, and they can come into a denomination.