² tn The clause beginning with ὅτι (Joti) is often taken as (1) epexegetical or (2) appositional to the commandment (ἐντολήν, entolhn) giving a further explanation or clarification of it. But the statement following the ὅτι is about light and darkness, and it is difficult to see how this has anything to do with the commandment, especially as the commandment is related to the “new commandment” of John 13:34 for believers to love one another. It is far more likely that (3) the ὅτι clause should be understood as causal, but this still does not answer the question of whether it offers the reason for writing the “new commandment” itself or the reason for the relative clause (“that is true in him and in you”). It probably gives the reason for the writing of the commandment, although R. E. Brown (Epistles of John [AB], 268) thinks it refers to both.