I want to stop here for a moment to look at truth. Should the word truth be capitalized here because it is a person? I just finished reading that the Holy Spirit is truth. John says this in chapter five of this letter. I like the symmetry of this part of the Greek sentence which goes ‘because the Spirit is the truth.’ John makes them both definite. He does not say ‘the Spirit is a truth’ but says He is the truth.
Of course John also reports to us what Jesus said of Himself, “I am the way, and the truth, and the life.” (John 14:6). The closest that John comes to this for God the Father is,’that the God truthful is.’
I think that this part of the letter is saying that if we live in the light, in right living like Jesus, then we are following the Truth and we can have deeply caring and practical relationships.
There is a lot to discuss here in these short three verses. The ‘then’ that starts the last sentence bothers me a bit. Need to look into it.