1 John 1:7

Compare Eph 5:8, Eph 5:11-14. "WE WALK"; "God is (essentially in His very nature as 'the light,' Jo1 1:5) in the light." WALKING in the light, the element in which God Himself is, constitutes the test of fellowship with Him. Christ, like us, walked in the light (Jo1 2:6). ALFORD notices, Walking in the light as He is in the light, is no mere imitation of God, but an identity in the essential element of our daily walk with the essential element of God's eternal being. we have fellowship one with another--and of course with God (to be understood from Jo1 1:6). Without having fellowship with God there can be no true and Christian fellowship one with another (compare Jo1 1:3). and--as the result of "walking in the light, as He is in the light." the blood of Jesus . . . cleanseth us from all sin--daily contracted through the sinful weakness of the flesh, and the power of Satan and the world. He is speaking not of justification through His blood once for all, but of the present sanctification ("cleanseth" is present tense) which the believer, walking in the light and having fellowship with God and the saints, enjoys as His privilege. Compare Joh 13:10, Greek, "He that has been bathed, needeth not save to wash his feet, but is clean every whit." Compare Jo1 1:9, "cleanse us from all unrighteousness," a further step besides "forgiving us our sins.

— Jamieson-Fausset-Brown Commentary (public domain)