John Gill Commentary Romans 1:31

"without understanding, covenant-breakers, without natural affection, unmerciful:" — Romans 1:31 (ASV)

Without understanding
Of God, of his nature and worship, of things divine and even moral, being given up to a reprobate mind:

covenant breakers ;
had no regard to private or public contracts:

without natural affection ;
to their parents, children, relations and friends:

implacable ;
when once offended there was no reconciling of them:

unmerciful ;
had no pity and compassion to persons in distress.