Here are some descriptions of unmerciful pastors.
They preach for money, not love:
Evil ministers are such as have no bowels to the souls of their people. They do not pity them or pray for them. They seek not them but theirs. They preach not for love but for lucre. Their care is more for tithes than four souls. How can they be called spiritual fathers, who are without bowels? These are mercenaries, not ministers
They don’t preach the Bible:
They are unmerciful to souls who, instead of breaking the bread of life, fill their people’s heads with airy speculations and notions; who rather tickle the fancy than touch the conscience and give precious souls rather music than food.
They preach above their people:
Some ministers love to soar aloft like the eagle and fly above their people’s capacities, endeavoring rather to be admired than undersood.
Ministers should be stars to give light not clouds to obscure the truth.
Source: Thomas Watson, The Beatitudes, p.146
Note: Watson uses the word bowels for compassion and mercy.