If we say that we have no sin, we deceive ourselves, and the truth is not in us. Confession of sins flows from 'walking in the light' (1 John 1:7). 'If thou shall confess thyself a sinner, the truth is in thee; for the truth is light. Not yet has thy life become perfectly light, as sins are still in thee; yet thou hast already begun to be illuminated, because there is in thee confession of sins' (Augustine).
That we have no sin. "HAVE," not 'have had,' must refer, not to the past life while unconverted, but to the present state, wherein believers have sin even still. "Sin" is singular; "(confess our) sins," 1 John 1:9, plural. Sin means the corruption of the old man still in us, and the stain created by actual sins flowing from that old nature. To confess our need of cleansing from present sin is essential to 'walking in the light;' so far is the presence of sin incompatible with our in the main 'walking in light.' But the believer hates, confesses, and longs to be delivered from all sin, which is darkness. 'They who defend their sins will see in the great day whether their sins can defend them.'
Deceive ourselves - not God (Galatians 6:7): we only make ourselves to err.
The truth - (1 John 2:4.) True faith. 'The truth respecting God's holiness and our sinfulness, the first spark of light in us, has no place in us' (Alford).