In [Christ] is no sin.
Here is the third testimony to the Lord’s absolute perfection and sinlessness. John perhaps knew the Lord better than any of the other apostles. He enjoyed a deep, open relationship with the Lord and knew the Lord’s heart. His witness is that the Lord had no sin in Him. There was no root of sin, no sinful nature. Not only did He not do any sin, or know any sin, there just wasn’t any sin in Him. Therefore He could not have sinned. We have a perfect, sinless, non-sinable Savior.