Some helpful words:
Christ's death involves placating God's wrath that was directed against us. Christ himself endured it in our place. In one sense penal substitution includes the ideas of both expiation (the removal of the guilt of sin) and propitiation (appeasing God's wrath).
Because Christ took our place in obeying the Father and in suffering for our sins and because he appeased the wrath of God that stood against us, so he removed all barriers to a restored friendship with him. We are now in harmony with God through the atoning work of Christ.
Robert Letham, The Work of Christ, p. 140, 144
My contention is that "substitution" is not a further "theory" or "image" to be set alongside the others, but rather the foundation of them all, without which each lacks cogency. If God in Christ did not die in our place, there could be neither propitiation, nor redemption, nor justification, nor reconciliation.
John Stott, The Cross of Christ, p. 156