"Insight one concerns God; it is that the retributive principle has his sanction, and indeed expresses the holiness, justice and goodness reflected in his law, and that death, spiritual as well as physical, the loss of the life of God as well as that of the body, is the rightful sentence which he has announced against us, and now prepares to inflict.Insight two concerns ourselves: it is that, standing thus under sentence, we are helpless either to undo, the past or to shake off sin in the present, and thus have no way of averting what threatens.Insight three concerns Jesus Christ: it is that he, the God-man of John 1:1-18 and Hebrews 1-2, took our place under judgment and received in his own personal experience all the dimensions of’ the death that was our sentence, whatever these were, so laying the foundation for our pardon and immunity.‘We may not know, we cannot tell
What pains he had to bear;
But we believe it was for us
He hung and suffered there.’Insight four concerns faith: it is that faith is a matter first and foremost of looking outside and away from oneself to Christ and his cross as the sole ground of present forgiveness and future hope. Faith sees that God’s demands remain what they were, and that God’s law of retribution, which our conscience declares to be right, has not ceased to operate in his world, nor ever will; but that in our case the law has operated already, so that all our sins, past present and even future, have been covered by Calvary."J.I. Packer on Penal Substitution