but if we [really] walk in the Light [that is, live each and every day in conformity with the precepts of God], as He Himself is in the Light, we have [true, unbroken] fellowship with one another [He with us, and we with Him], and the blood of Jesus His Son cleanses us from all sin [by erasing the stain of sin, keeping us cleansed from sin in all its forms and manifestations].

And He [that same Jesus] is the propitiation for our sins [the atoning sacrifice that holds back the wrath of God that would otherwise be directed at us because of our sinful nature—our worldliness, our lifestyle]; and not for ours alone, but also for [the sins of all believers throughout] the whole world.

whoever says he lives in Christ [that is, whoever says he has accepted Him as God and Savior] ought [as a moral obligation] to walk and conduct himself just as He walked and conducted Himself.

This is the promise which He Himself promised us—eternal life.

And everyone who has this hope [confidently placed] in Him purifies himself, just as He is pure (holy, undefiled, guiltless).

You know that He appeared [in visible form as a man] in order to take away sins; and in Him there is [absolutely] no sin [for He has neither the sin nature nor has He committed sin or acts worthy of blame].

The one who believes in the Son of God [who adheres to, trusts in, and relies confidently on Him as Savior] has the testimony within himself [because he can speak authoritatively about Christ from his own personal experience]. The one who does not believe God [in this way] has made Him [out to be] a liar, because he has not believed in the evidence that God has given regarding His Son.