Mankind, spiritually bankrupt, has nothing to offer, but God, prompted by pure grace, and drawing on his eternal wisdom, prepares a counsel of salvation in which the Father, the Son, and the Holy Spirit are united in redeeming love and pity for the human race. The triune God resolves to save the world, and to accept the good offices of a Mediator who shall act for mankind as their representative and suffer for them as their substitute: so accommodating is the divine will, and so predisposed to forgive our transgressions.
But the Three-in-One, acting to save the world, go further: they resolve that the salvation shall be free to the human race. It will cost them nothing. For them, it will be an act of pure love and mercy. From sinners as such no satisfaction will be required. Instead, everything will flow from the loving-kindness of God. He will bear the whole cost. He will provide the one who will take the sinner’s place.
But he will go even further: he will become the one who takes the sinner’s place. God the Son will suffer for the world’s sin. God the Father will suffer in the Son’s pain. God the Holy Spirit will share in the pain of both.
At Gethsemane and Golgotha the Three will be One, as God, not sparing himself, takes blood, his own blood, and sheds it to redeem the world.
–Donald Macleod, Christ Crucified: Understanding the Atonement (IVP, 2014), 177
(HT: Dane Ortlund)