A.T. Robertson Commentary 2 Peter 2:21

"For it were better for them not to have known the way of righteousness, than, after knowing it, to turn back from the holy commandment delivered unto them." — 2 Peter 2:21 (ASV)

It were better (κρειττον ην). Apodosis of a condition of second class without αν, as is usual with clauses of possibility, propriety, obligation (Matthew 26:24; 1 Corinthians 5:10; Romans 7:7; Hebrews 9:26).

Not to have known (μη επεγνωκενα). Perfect active infinitive of επιγινωσκω (cf. επιγνωσε, verse 20) to know fully.

The way of righteousness (την οδον της δικαιοσυνης). For the phrase see Mt 21:33, also the way of truth (2:2), the straight way (2:15).

After knowing it (επιγνουσιν). Second aorist active participle of επιγινωσκω (just used) in the dative plural agreeing with αυτοις (for them).

To turn back (υποστρεψα). First aorist active infinitive of υποστρεφω, old and common verb, to turn back, to return.

From (εκ). Out of. So in Ac 12:25 with υποστρεφω. With ablative case. See Ro 7:12 for αγια applied to η εντολη (cf. 1 Timothy 6:14). II Peter strikes a high ethical note (1:5ff.).

Delivered (παραδοθεισης). First aorist passive participle feminine ablative singular of παραδιδωμ.