Subject: Walking in Truth in the Context of Hospitality - 2 John

2 John 1:4
I rejoiced greatly to find some of your children walking in the truth, just as we were commanded by the Father.

Subject:  Walking in Truth

In the above verse the word "truth" is used for the fifth time already in this little letter to the church.   The context of the letter is that some false teachers (non-truth) were entering the church and abusing the natural hospitality of Christian believers and love to preach their false teachings.  John is writing to correct this.   Hence the emphasis on the "truth" in the opening remarks.   He wants this church to act in truth (faithful obedience to the teaching of Christ expressed in love for fellow believers).  He actually was pleased that some of them were "walking" in truth.   Note what MacArthur says about this term "walking" when referred to in the context of believers:

Walking is a frequent New Testament metaphor for the Christian life. Believers “walk in newness of life” (Rom. 6:4), “walk by faith, not by sight” (2 Cor. 5:7), “walk by the Spirit” (Gal. 5:16, 25), “walk in good works” (Eph. 2:10), “walk in a manner worthy of the calling with which [they] have been called” (Eph. 4:1), “walk in love” (Eph. 5:2), “walk as children of Light” (Eph. 5:8), “walk in wisdom” (Eph. 5:15), “walk in a manner worthy of the Lord, to please Him in all respects” (Col. 1:10), “walk in a manner worthy of the God who calls [them] into His own kingdom and glory” (1 Thess. 2:12), “walk in the same manner as [Jesus] walked” (1 John 2:6), and “walk according to His commandments” (2 John 6).

John doesn't simply want these believers to "believe" in the truth.  He wants them to "walk" in it ... practice it at all cost.  However, that does not mean assisting those who are anti-truth.   The letter is clear:  Truth should begat truth.  We are not to assist false teachers under the guise of "love and truth."   Those who hold to the truth they have in Christ must do everything to promote that truth.  That is what walking in the truth is all about.  But, we are NOT to assist, promote or be hospitable with those who teach false doctrine; non-truth.   Our walk in truth must promote more truth.