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 Titus 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 Luke 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 Jude 1:20; Galatians 1:23; Galatians 3:23; Philippians 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.