If we say that we have no sin, we deceive ourselves, and the truth is not in us. If we say that we have no sin - This is tantamount to 1 John 1:10 : If we say that we have not sinned. All have sinned, and come short of the glory of God; and therefore every man needs a Savior, such as Christ is. It is very likely that the heretics, against whose evil doctrines the apostle writes, denied that they had any sin, or needed any Savior. In deed, the Gnostics even denied that Christ suffered: the Aeon, or Divine Being that dwelt in the man Christ Jesus, according to them, left him when he was taken by the Jews; and he, being but a common man, his sufferings and death had neither merit nor efficacy.
We deceive ourselves - By supposing that we have no guilt, no sinfulness, and consequently have no need of the blood of Christ as an atoning sacrifice: this is the most dreadful of all deceptions, as it leaves the soul under all the guilt and pollution of sin, exposed to hell, and utterly unfit for heaven.
The truth is not in us - We have no knowledge of the Gospel of Jesus, the whole of which is founded on this most awful truth - all have sinned, all are guilty, all are unholy; and none can redeem himself. Hence it is as necessary that Jesus Christ should become incarnated, and suffer and die to bring men to God.