Propitiation and Expiation

I have been listening to a few talks on the Cross, by Don Carson, John Piper and Mark Driscoll. I've been really struggling to get my head around some of the terminology used, and to remember what this terminology refers to. I found some helpful summaries on Wikipedia about propitiation and expiation.

'In Christian theology, propitiation is the work of Jesus Christ on the cross, by which He fulfills the wrath of God (both an emotional response of anger and a moral response of indignation), and conciliates Him who would otherwise be offended by our sin and would demand that we pay the penalty for it.'

'Propitiation literally means to make favorable and specifically includes the idea of dealing with God’s wrath against sinners. Expiation literally means to make pious and implies either the removal or cleansing of sin.'

'The idea of propitiation includes that of expiation as its means, but the word "expiation" has no reference to quenching God’s righteous anger. The difference is that linguistically the object of expiation is sin, not God (that is, sin is removed, not God). Linguistically, one propitiates a person (makes them favorable), and one expiates a problem (removes it). Christ's death was therefore both an expiation and a propitiation. By expiating (removing the problem of) sin God was made propitious (favorable) to us.'