'In the Light' in the Bible

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].

The one who says he is in the Light [in consistent fellowship with Christ] and yet habitually hates (works against) his brother [in Christ] is in the darkness until now.

The one who loves and unselfishly seeks the best for his [believing] brother lives in the Light, and in him there is no occasion for stumbling or offense [he does not hurt the cause of Christ or lead others to sin].