John believes in a knowable salvation. Light and knowledge are inseparable. We may know because God gives light. This certainty has a definite bearing upon our conduct. Love is also a vital part of the evidence.
Additional proof is advanced by reference to the absence or presence of sin.
The children of God are free from sin and sinning. Sinning is not viewed as an impossibility. Any man may sin, most men do sin, but no man has to sin. Man's deportment is evidence of deliverance from sin. Every path pursued in this Epistle leads to the same conclusion.