1 John 4:6

He that knoweth [ο γ ι ν ω σ κ ω ν]. Lit., the one knowing : he who is habitually and ever more clearly perceiving and recognizing God as his Christian life unfolds. The knowledge is regarded as progressive and not complete. Compare Philippians 3:12, and He who is calling (oJ kalwn, 1 Thessalonians 5:24) also oJ ajgapwn he that loves (ver. 7).

Hereby [ε κ τ ο υ τ ο υ]. Not the same as the common ejn toutw (ver. 2). It occurs only here in the Epistle. En toutw is in this : ejk toutou from this. The former marks the residing or consisting of the essence or truth of a thing in something the apprehension of which conveys to us the essential nature of the thing itself. The latter marks the inference or deduction of the truth from something, as contrasted with its immediate perception in that something. Rev., by this.

The spirit of error [τ ο π ν ε υ μ α τ η ς π λ α ν η ς]. The phrase occurs nowhere else in the New Testament. Compare pneumasi planoiv misleading spirits, 1 Timothy 4:1.