Mercy has come to prominence through the pontificate of Pope Francis, but what is mercy and how do different denominations and faiths understand the term. This is our starting point, an exploration of the universality of the term particularly as a possible communion across the Abrahamic faiths. Biblical injunctions concerning mercy prefigure a focus on Pope Francis' elevation of the discourse on mercy. A key principle of mercy for this Pope is the use of dialogue and here we see how the work of Romano Guardini is a significant influence. Discernment is named as an operative tool of mercy and we consider the impact of an lgnatian fonmation on the promotion of mercy. Christological lynchpins for mercy emerge from a consideration of 'Evangelii Gadium'; and here we also encounter the Trinitarian horizon for mercy and indeed a possible Trinitarian ontology of mercy. Finally the ecclesiological ramifications and the geo-political impact of mercy conclude our investigation into why mercy is an ecclesiological imperative.