Thomas G. Casey (“As gentle rain from Heaven”, 15 March) identifies God’s mercy as a ­central theme for Pope Francis, and laments that “we have not yet managed to formulate a ­theology that has the mercy of God at its centre”. However, when he himself tries to define “mercy” he seems instead to describe patience; suggesting that God is merciful because punishment for uncooperative sinners is withheld for longer than might reasonably be expected. When this patience eventually runs out, mercy evaporates and God is once more revealed to be a coercive and punishing ­figure. Could it be the case that God’s mercy is profoundly challenging and perplexing for us precisely because its unconditionality and implied vulnerability scandalise