What is the biblical basis for the concept of substitution in salvation?

Substitution is a foundational aspect of atonement in Christian doctrine, illustrated in the sermon by Paul's plea for Onesimus in Philemon (Philemon 1:18). Here, Paul asks Philemon to charge Onesimus' debt to his own account, mirroring what Christ has done for us. In 2 Corinthians 5:21, we learn that God made Christ, who knew no sin, to be sin for us, so that we might become the righteousness of God in Him. This substitutionary atonement underscores the gravity of our sin and the magnitude of Christ's sacrifice. It shows that no matter how unworthy we may feel, Christ has taken our place, enabling us to be reconciled to God.