How do we know Jesus' atonement for sins is effective?

The effectiveness of Jesus' atonement is grounded in His identity as the sinless Lamb of God, who was manifested for the specific purpose of taking away our sins (1 John 3:5). By living a life without sin and willingly offering Himself as a sacrifice for our transgressions, He perfectly fulfilled the demands of God's law. Romans 8:3-4 assures us that God's justice was satisfied in Christ's death, and through Him, the righteous requirement of the law is fulfilled in those who believe, confirming the certainty of our salvation.