You are of your father the devil, and your will is to do your father's desires. He was a murderer from the beginning, and does not stand in the truth, because there is no truth in him. When he lies, he speaks out of his own character, for he is a liar and the father of lies (Jn 8:44).
Who is the liar but he who denies that Jesus is the Christ? This is the antichrist, he who denies the Father and the Son (1 Jn 2:22).
Little children, keep yourselves from idols (1 Jn 5:21).
i) In his influential article on "The Sanctity of Truth," John Murray takes the position that lying is intrinsically wrong. His argument relies heavily on the concept of alethinos in Johannine usage. However, I think he fails to capture the nuance of the alethinos word-group in Johannine theology.
Translations commonly render alethinos as "truth". Although "truth" is a valid translation, lexicographers include "genuine" or "real" as alternative definitions. So the traditional rendering prejudges the meaning of the term.
ii) In addition, we need to distinguish between the meaning of words and the meaning of concepts. What is John's concept of alethinos? In context, I don't think it means propositional truth, although that's covered. Rather, John uses alethinos as an antonym for what is counterfeit. For John, there's a dualism between what's authentic or genuine, on the one hand, and what's spurious or counterfeit, on the other.
iii) But even though that's semantically valid, it's too generic to capture the underlying concept, which is more specific. What makes something authentic or inauthentic? That involves the ultimate contrast between God and whatever denies God or supplants God. God is the standard of comparison. What God is like. What he says and does.
Satan and idolatry are the antithesis of alethinos. Satan is a usurper. Pagan deities usurp the real God. Idolatry is delusive.
An idolater or heretic doesn't merely deny the truth. He misrepresents God. He replaces God with something else.
iv) This has a propositional dimension, but it also has an existential dimension. An authentic life tracks the reality of God. An inauthentic life deviates from the reality of God.
v) Suppose you care for a senile relative. She's forgotten that her parents are dead. She's forgotten that her husband is dead. Everyday she asks about them. Where are they? Why doesn't she see them?
Should you tell her they are dead? She will forget. Telling her they are dead makes her repeatedly relive their death every day, or several times a day. Imagine the shock and trauma of hearing that time and again as if for the very first time. What could be more cruel?
Is it not better to tell her a comforting lie? They are shopping. They will be back soon.
That's not contrary to the Johannine concept of alethinos. In fact, that's consistent with the Johannine concept of alethinos. Acting in a way that's consonant with God's compassion, mercy, and lovingkindness.
That may ruffle some feathers, but sometimes we need to reexamine a traditional interpretation.