Who also made us sufficient for such confidence (hos kai hikanōsen hēmas). Late causative verb from hikanos (2Co 3:5) first aorist active indicative, “who (God) rendered us fit.” In N.T. only here and Col 1:12.
As ministers of a new covenant (diakonous kainēs diathēkēs). Predicate accusative with hikanōsen. For diathēkē see note on Mat 26:28 and for diakonos see note on Mat 20:26 and for kainēs (fresh and effective) see Luk 5:38. Only God can make us that.