Substitution is Christ, the Just One, standing in the place of the unjust so that He may bring them to God.
At the heart of the cross is an exchange: the sinless Son takes the place of sinners, bearing what they deserved so that they may receive what He deserved. He who knew no sin was made sin for us, that we might be made the righteousness of God in Him.
This is not an unwilling victim punished by a reluctant Father, but the Son freely giving Himself in love, in perfect accord with the Father who sent Him. Substitution is normally held together with propitiation: Christ bears sin’s judgment in the sinner’s place, and so the just dies for the unjust to bring us home.
See in Scripture: Isaiah 53:4–6; Romans 5:6–8; 2 Corinthians 5:21; Galatians 3:13; 1 Peter 2:24; 1 Peter 3:18