A.T. Robertson Commentary Jude 1:3

"Beloved, while I was giving all diligence to write unto you of our common salvation, I was constrained to write unto you exhorting you to contend earnestly for the faith which was once for all delivered unto the saints." — Jude 1:3 (ASV)

Beloved (αγαπητο). As in 3 John 1:2.

All diligence (πασαν σπουδην). As in 2 Peter 1:5.

Of our common salvation (περ της κοινης ημων σωτηριας). See this use of κοινος (common to all) in Tit 1:4 with πιστις, while in 2 Peter 1:1 we have ισοτιμον πιστιν, which see.

I was constrained (αναγκην εσχον). "I had necessity" like Lu 14:18; Hebrews 7:27.

To contend earnestly (επαγωνιζεσθα). Late and rare (in Plutarch, inscriptions) compound, here only in N.T. A little additional (επ) striving to the already strong αγωνιζεσθα (αγων contest). Cf. 1 Timothy 6:12 αγωνιζου τον καλον αγωνα.

For the faith (τηι--πιστε). Dative of advantage. Here not in the original sense of trust, but rather of the thing believed as in verse 20; Galatians 1:23; 3:23; Php 1:27.

Once for all delivered (απαξ παραδοθειση). First aorist passive participle feminine dative singular of παραδιδωμ, for which see 2 Peter 2:21. See also 2 Thessalonians 2:15; 1 Corinthians 11:2; 1 Timothy 6:20.