4 Wherefore also the Apostle says: “What will you, shall I come to you with a rod, or in love and in the spirit of gentleness?” First he made mention of the rod, and like the almond rod struck those who were wandering, that he might afterwards comfort them in the spirit of meekness. And so meekness restored him whom the rod had deprived of the heavenly sacraments. And to his disciple he gave similar injunctions, saying: “Reprove, beseech, rebuke.” Two of these are hard, one is gentle, but they are hard only that they may soften; for as to suffering from excess of gall, bitter food or drink seems sweet, and on the other hand sweet food is bitter, so where the mind is wounded it grows worse under the influence of pleasurable flattery, and again is made sound by the bitterness of correction.
Source: Letters (New Advent)