Cross Friday - Packer on Penal Substitution as a "model"

In What did the Cross Achieve? The Logic of Penal Substitution, J.I. Packer's magisterial lecture/booklet on Penal Substitution (the doctrine that Jesus died for our sins), Packer says the following about penal substitution as a model ("model", for Packer, is something that communicates truth about God - but remembers that it cannot communicate the whole truth - and which Packer states is basically the only way we can talk about any aspect of God):

It will by now be clear that those who affirm penal substitution offer this model not as an explanatory analysis of what lay 'behind' Christ's atoning death in the way that the laws of heat provide an explanatory analysis of what lies 'behind' the boiling of a kettle, but rather as a pointer directing attention to various fundamental features of the mystery - that is, according to our earlier definition, the transcendent and not-wholly-comprehensible divine reality - of Christ's atoning death itself, as the New Testament writers declare it. Most prominent among these features are the mysterious divine love which was its source, and of which it is the measure (cf. Rom. 5:8; 1 John 4:8-10; John 15:13); the mysterious necessity for it, evident from Paul's witness in Romans 8:32 that God did not spare his Son, but gave him up to death for us, which shows that, he being he, he could not have saved us at any less cost to himself; the mysterious solidarity in virtue of which Christ could be 'made sin' by the imputing to him of our answerability, and could die for our sins in our place, and we could be 'made righteous' before God through faith by the virtue of his obedience (cf. Rom. 5:17-19, 3 Cor 5:21 [sic]); and the mysterious mode of union whereby, without any diminution of our individuality as persons, or his, Christ and we are 'in' each other in such a sense that already we have passed with him through death into risen life. Recognition of these mysteries causes no embarrassment, nor need it; sicne the cross is undeniably central in the New Testament witness to God's work, it was only to be expected that more dimensions of mystery would be found clustered here than anywhere. (Indeed, there are more than we listed; for a full statement, the tri-unity of the loving God, the incarnation itself, and God's predestining the free acts of his enemies, would also have to come in.) To the question, what does the cross mean in God's plan for man's good, a biblical answer is ready to hand, but when we ask how these things can be we find ourself facing mystery at every point.

An interesting quote - and one which I want to think more about. Anyone agree/disagree and want to give reasons?

(Also, note that due to taking too long this post is not on late friday night, but very early on saturday!)