I'm delighted to see that George Smeaton's two volumes on the doctrine of atonement are back in print. Many thanks to the Banner of Truth Trust for doing this.
Check out Christ's Doctrine of the Atonement and the Apostles' Doctrine of the Atonement
Here are some gems:
Jesus was visited with penal suffering because he appeared before God only in the guise of our accumulated sin; not therefore as a private individual, but as a representative; sinless in himself, but sin covered; loved as a Son, but condemned as a sin-bearer, in virtue of that federal union between him and his people, which lay at the foundation of the whole. Thus God condemned sin in the flesh, and in consequence of this there is no condemnation to us.
Were the atonement not the principal matter of the gospel, and the highest exhibition of the united wisdom, love and faithfulness of God,--in a word, the greatest act of God in the universe,--that terrible anathema on its subverters would seem to us something inexplicable, if not intolerable. But the doom is justified by the nature of Christ's death, and by the great fact of the atonement.