1 John Chapter 1, Verse 6
From BibleWiki
6: εαν ειπωμεν οτι κοινωνιαν εχομεν μετ αυτου και εν τω σκοτει περιπατωμεν ψευδομεθα και ου ποιουμεν την αληθειαν
6: If we say that we have fellowship with him, and walk in
darkness, we lie, and do not the truth:
6: If we say that we have fellowship with him and walk in darkness, we
lie and do not the truth.
If we say that we have fellowship with him. If we reckon ourselves among his friends, or, in other words, if we profess to be like him: for a profession of religion involves the idea of having fellowship with God, "1Jn 1:3, and he who professes that should be like him.
And walk in darkness. Live in sin and error. To "walk in darkness" now commonly denotes to be in doubt about our religious state, in contradistinction from living in the enjoyment of religion. That is not, however, probably the whole idea here. The leading thought is, that if we live in sin, it is a proof that our profession of religion is false. Desirable as it is to have the comforts of religion, yet it is not always true that they who do not are not true Christians, nor is it true by any means that they intend to deceive the world.
We lie. We are false professors; we are deceived if we think that we can have fellowship with God, and yet live in the practice of sin. As God is pure, so must we be, if we would be his friends. This does not mean necessarily that they meant to deceive, but that there was an irreconcilable contradiction between a life of sin and fellowship with God.
And do not the truth. Do not act truly. The profession is a false one. Compare "Jn 3:22". To do the truth is to act in accordance with truth.

