Walk (Gk. περιπατέω, peripateo). (4; Matt 11:5; Rom 13:13; 2 Cor 4:2; Gal 5:16; Eph 2:10) Strong’s 4043
This word, meaning to “walk,” is common in the NT. It is often used literally, but is also commonly used metaphorically to refer to one's “conduct,” or “manner of life.” To “walk in the truth” is to live in such a way as to reflect an understanding and faithful acceptance of the truth, and thus to flesh out the truth by example. The truth John refers to here is clearly Christian truth, the gospel, the truth about Jesus, God and indeed the readers and all humanity. One might say today, biblical truth.