Again, I write a new commandment to you, which is true in him and in you; because the darkness is passing away, and the true light already shines.
which thing is true in him and in you: "Which thing" refers to the abstract truth or fact that the old commandment is new in quality and meaning. "True" is from alethes, meaning "primarily, unconcealed, manifest...actual, true to fact" (Vine 158). This fact of a new quality of love becomes real in Christ and in the Christian readers. Alford renders it "...this is true both in (the case of) Him (Christ) and in (the case of) you" (438). The reality of this love was manifested in Jesus and continues to be expressed in the lives of all who imitate His example.