Crossing Cultural Frontiers (Orbis). It is deep and well thought out but approachable and inspiring. With the significant focus I have had on the refugee crisis and migration in general, I was particularly attracted to his chapter "Toward a Theology of Migration.
He describes the centrality of this human pattern in this way, "Migration receives no single, defining treatment in Genesis, but the book offers so many examples of migration that the reader is left in no doubt that it is one of the constants in human life." (pg. 52)
Walls paints a picture over all of human history showing the movements of civilizations and how God has utilized each of these movements for His glory. I especially appreciated his distinction between Adam's migration out of the Garden of Eden and Abraham's migration to the Promised Land. Walls describes the Adamic migrations as "involuntary and punitive" and the Abrahamic migrations as "voluntary and hope driven." History is a ebbing and flowing of these two types of migrations as God exerts discipline and rewards faith.
This migration framework is helpful as we look at the migrant crisis of the 21st Century where over 65 million are forcibly on the move with hundreds of millions more moving to find a better life.
The main insight I was left with was that God is working through each of these movements to bring us into deeper relationship with Him. What a powerful reminder even in these liminal moments.