Why do we need a substitute for our sins?

In Reformed theology, the concept of substitutionary atonement is central to understanding the gospel. Due to humanity's sinfulness and God's holiness, we are under the curse of the law, as stated in Romans 6:23 where the wages of sin equals death. In God's mercy, He provided Christ as our substitute, who bore the penalty of our sins and satisfied God's justice. This substitution allows believers to be declared righteous before God, as Christ's obedience fulfills the requirements of the law on our behalf, thus highlighting the necessity of a substitute in the redemptive plan.