1 John 2:25 New English Translation

²⁵Now this^[a] is the promise that he^[b] himself made to^[c] us: eternal life.^[d]

1 John 2:25 tn It is difficult to know whether the phrase καὶ αὕτη ἐστιν (kai hautē estin) refers (1) to the preceding or (2) to the following material, or (3) to both. The same phrase occurs at the beginning of 1:5, where it serves as a transitional link between the prologue (1:1-4) and the first major section of the letter (1:5-3:10). It is probably best to see the phrase here as transitional as well; thus καί (kai) has been translated “now” rather than “and.” The accusative phrase at the end of v. 25, τὴν ζωὴν τὴν αἰώνιον (tēn zōēn tēn aiōnion), stands in apposition to the relative pronoun ἥν (hēn), whose antecedent is ἡ ἐπαγγελία (hē epangelia; see BDF §295). Thus the “promise” consists of “eternal life.”
1 John 2:25 tn The pronoun could refer to God or Jesus Christ, but a reference to Jesus Christ is more likely here.
1 John 2:25 tn Grk “he himself promised.” The repetition of the cognate verb “promised” after the noun “promise” is redundant in English.
1 John 2:25 sn The promise consists of eternal life, but it is also related to the concept of “remaining” in 2:24. The person who “remains in the Son and in the Father” thus has this promise of eternal life from Jesus himself. Consistent with this, 1 John 5:12 implies that the believer has this eternal life now, not just in the future, and this in turn agrees with John 5:24.

New English Translation (NET)