John uses the word “truth” four times in the opening three verses of 2 John. Truth is fourfold, stretching out to the four corners of the earth. It also seems possible to take “truth” here, at least at a secondary level, as a reference to Christ – especially in the phrase “in truth,” “knowing truth,” and “for the sake of the truth” (vv. 1-2). Christ, the Way, Truth, and Life, also stretches to the four corners of the earth.
And with the Truth goes the commandment of God: John uses the word “commandment” four times in verses 5-6. The commandment is what the church is to proclaim to all nations, so that the Great Commission will be fulfilled as Gentiles come to the “obedience of faith.”