3 Beloved, while I was very diligent to write to you concerning our common salvation, I found it necessary to write to you exhorting you to contend earnestly for the faith which was once for all delivered to the saints. 4 For certain men have crept in unnoticed, who long ago were marked out for this condemnation, ungodly men, who turn the grace of our God into lewdness and deny the only Lord God and our Lord Jesus Christ. (Jude 3–4, NKJV)
Jude calls upon at least two incentives to urge Christians to agonize intensely (“contend earnestly”) for the faith (the gospel, Gal. 1:11, 23). First, it is because of the gospel that we share a common salvation (Rom. 1:16-17). And next, because God has delivered the faith to us with finality (“once for all”). Precisely because the gospel is powerful to save us, and because God has fully delivered this powerful gospel to us, we must fight for it against all who would attempt to dilute its power and impugn its adequacy to save us (see verse 4). To reject the gospel’s salvation and its fullness of grace brings one under the condemnation of the ungodly. Instead, let us give our full strength and energy to guarding and advancing the truth of the gospel.