I think the translation: ‘be merciful to me’ masks the concept contained in the Greek word used here.  It is not the usual word ‘have mercy’ but the word for atone or propitiate.  So then, the prayer for mercy is a prayer that God may remove his wrath from the tax-collector, a sinner.

True, the concept of sacrifice is not found here, but I think there is a strong case to argue the normal meaning of the word (ilastheti) is found in Luke 18, as acknowledged by a significant number of commentators, including Leon Morris, whose work on the propiation word group has been very important. 

All this strengthens your point, Lionel, for the ground for God to be propitiated in the Bible is his mercy, not our acts of rightousness.

Thanks for your article Lionel. 
Would you mind clarifying a question I have?
I think you are right to suggest teh use of the propitiation word in, say 1 John 4, where it is a noun, includes both the turning aside of God’s wrath and, therefore, the covering of sin (expiation).

But in Luke 18, where the verb is used, are you suggesting the idea here includes more than a request God turn his anger aside from the tax-collector, a sinner?  Are you suggesting that he is asking for a sacrifice to be made to achieve this? 

If so, I wonder if that is to commit a linguistic error. That is, is that to take what seems to be true of the word used as a noun elsewhere to be true of the verbal form used in this prayer, where the context does not take one in the direction of a sacrifice? 

It is true that Luke 18 is part of the travel narrative, and, as such, we the reader know that in Jerusalem Jesus will in fact provide the sacrifice that will make what the tax collector asks for possible (God’s wrath to be turned aside).  But I wonder if the word itself as used in Luke 18 means more than: God, remove your wrath from me, a sinner?

I’d love to have your thoughts on this.  Thanks again for the excellent articles on key terms as they are used in the Bible.

Sounds like the Tax Collector and Cranmer had a few things in common… From the Homily on Salvation:

“So that the true understanding of this doctrine -We be justified freely by faith
without works, or that we be justified by faith in Christ only - is not, that this
our own act, to believe in Christ,or this our faith in Christ, or this our faith in
Christ, which is within us, doth justify us, and deserve our justification unto us
- for that were to count ourselves to be justified by some act or virtue that is
within ourselves - but the true understanding and meaning thereof is, that,although we hear God’s word and believe it; although we have faith, hope,
charity, repentance, dread, and fear of God within us, and do never so many good works thereunto; yet we must renounce the merit of all our said virtues, of faith, hope, charity, and all our other virtues and good deeds, which we either have done, shall do, or can do, as things that be far too weak and insufficient, and imperfect, to deserve remission of our sins, and our
justification.”

Ashley Null nailed this in our Church History lecture this morning.  An absolute cracker!

When will you continue this excellent series?

It is a wonderfully clear presentation.