Charles Spurgeon on the Gospel: Substitutionary Atonement

Charles Spurgeon wrote in his Autobiography: 

I have always considered, with Luther and Calvin, that the sum and substance of the gospel lies in that word Substitution–Christ standing in the stead of man. If I understand the gospel, it is this: I deserve to be lost forever; the only reason I should not be damned is this, that Christ was punished in my stead, and there is no need to execute a sentence twice for sin.