How do we know that Christ is our representative?

In Reformed theology, Jesus Christ is referred to as the 'last Adam' who came to rectify the fall that occurred through the first Adam. Romans 5:19 emphasizes this by stating that 'For as by one man's disobedience many were made sinners, so by the obedience of one shall many be made righteous.' Christ's obedience, culminating in His sacrificial death, serves as a substitute for the disobedience of Adam. As the elect of God, those who are united to Him by faith share in His righteousness, thus restoring the relationship that was severed by sin. His life and death fulfill the law that Adam broke, ensuring that all who are in Him are declared righteous before God.