God’s glory and his name consist fundamentally in his propensity to show mercy and his sovereign freedom in its distribution. Or to put it more precisely, it is the glory of God in his essential nature mainly to dispense mercy (but also wrath, Exodus 34:7) on whomever he pleases apart from any constraint originating outside his own will. This is the essence of what it means to be God. This is his name.
John Piper on Exodus 33:18-19 from The Justification Of God