If we confess our sins before God, then He will offer complete forgiveness at that very instant. His forgiveness comes with the purification of our souls. We simply need to accept that proposition as true. That is how we secure an objective basis for our assurance of salvation.
If we can place enough trust in a park bench to support our body weight every time that we sit on one, then how much more are we able to place our trust in God and His work for forgiveness and redemption? God is our infallible support. In Him exists no deceit.
The Apostle John describes in succinct terms how the atonement of Jesus Christ is applied to those who believe on His name for eternal life. It is applied to us on a day by day basis.