Must God punish sin?

Few Christians are willing to do any sustained thinking about sin. Of course, evangelical preachers will mention it from time to time. After all, they need to convince their hearers that they are ‘sound’. But they will feel under intense pressure from those same hearers to move quickly and as smoothly as possible from anything to do with sin and judgment to a positive and uplifting message about God’s love.
The fact is, that for most modern Christians the doctrine of the love of God has become the one great ‘givens’, the unargued and unarguable axiom. It then becomes the lens through when everything else must be viewed. It all comes dangerously close to taking God’s love for granted, of assuming, “Of course God loves us – that’s his job.”
But the love of God should not be viewed as obvious. It should be viewed, rather, as a great and glorious surprise. What should be obvious to us is that there is a creator-God who made us and to whom we are accountable. Between his perfect uprightness and our abject fallenness there is a terrifying chasm. We should not wonder that our sins deserve punishment. We should wonder how anything or anyone could bridge that chasm.
But this raises the question: why does not God, being God, simply choose to overlook human sin? Why does he require either that we suffer punishment for our sins, or that Someone Else suffer that punishment on our behalf?
Of course, some Christians will argue that God does choose to overlook sin. At least, they will argue that when that Someone Else (namely Christ) died, it was not to suffer the penalty for our sins. There is, for such brethren, no penal aspect to the atonement.
I have reflected elsewhere on my conviction that the penal element is integral to a biblical doctrine of the atonement, and I will not repeat the arguments here.
But I would like to ponder the closely-related question: Must God punish sin?
Intuitively, we might reckon that God can do anything, and that he can therefore freely choose to punish sin or not to punish it, as he please. We might then ask: If God is love, why does he not choose not to punish sin? Or, at least, choose for that punishment not to be eternal? If a loving God is to punish sin, why cannot this always be with a view to restoration of the sinner. This line of argument was followed by the Socinians and was opposed by John Owen.
My brief answer would be to make the counter-intuitive assertion that God cannot do anything. As the Puritans used to say, there are three things that even God cannot do: God cannot lie, he cannot die, and he cannot deny himself. Now it is this last impossibility (God cannot deny himself) which is relevant here. For God’s love to merely ‘trump’ his justice would be for him to deny himself; for one aspect of his moral nature to contradict another aspect. Conscience teaches us that God is just. The Word of God teaches us that God is love. The first quality tells us that God must punish sin, and the second tells us that he has provided the means whereby the punishment that was due to us has been lifted from us and borne by Another.
I intend to read and think more deeply about this, and plan to use Ben Cooper’s study to help me.