64 The noun truth here has been interpreted in various ways: (1) There are a number of interpreters who understand the final noun in this series, truth (ἀληθείᾳ, alētheia) in an adverbial sense (“truly” or “in sincerity”), describing the way in which believers are to love. If the two pairs of nouns are compared, however, it is hard to see how the second noun with tongue (γλώσσῃ, glōssē) in the first pair can have an adverbial sense. (2) It seems better to understand the first noun in each pair as produced by the second noun: Words are produced by the tongue, and the (righteous) deeds with which believers are to love one another are produced by the truth.

In other versions

Little children, let us not love in word or talk but in deed and in truth.

Dear children, let us not love with words or speech but with actions and in truth.

Little children, let us not love in word or speech, but in action and in truth.

Dear children, let’s not merely say that we love each other; let us show the truth by our actions.

Little children, let us not love with word or with tongue, but in deed and truth.

My little children, let us not love in word, neither in tongue; but in deed and in truth.

Public Domain