Romans 1:31

Without understanding — i.e., without moral or spiritual understanding; incapable of discriminating between right and wrong, expedient and inexpedient. St. Paul prays that the Colossians may possess this faculty (Colossians 1:9).

Without natural affection. — The affection founded upon natural relationship — e.g., between parent and child, husband and wife, brother and sister. In illustration of this particular expression, we may remember that infanticide and divorce were very common at this period.