If you believe at all in the doctrine of the wrath of God against sin, then obviously sin must be punished. What comes in and that leads to the necessity of substitution.
…You and I must realise that; that before we see the love of God in the cross we must see His wrath. The two things are always together and you cannot separate them. It is only as you have some conception of the depth of His wrath that you will understand the depth of His love. It was God Himself who found the way whereby His own wrath could express itself against sin, and yet the sinner not be destroyed but rather justified, because His own Son had borne the punishment.
…He [God] made Him [Jesus Chris] sin, He imputed the guilt of our sins to Him; He put them upon Him; and then He tells us that He punished them in Him. Any idea or theory of the atonement must always give full weight and significance to the activity of God the Father.
…There is only one doctrine of the atonement, not only in the Bible, but which is true to the biblical revelation concerning the character of God. God’s love, let us never forget, is a holy love. I say it to the glory of God—that God cannot forgive anybody by just saying, ‘I am going to forgive’. He cannot. There was only one way in which God could forgive: it was by putting our sins on His Son and by punishing them in Him. He poured out the vials of His wrath against sin on His own Son. He has ‘set him forth as a propitiation’. God has done it. That is His severity working with his goodness—the two together. It is a holy love; It is a righteous forgiveness.*
*Sargent, T. (2007). Gems from Martyn Lloyd-Jones: An Anthology of Quotations from ‘the Doctor’ (15-16). Milton Keynes, England; Colorado Springs, CO; Hyderabad, AP: Paternoster.