"My Lord Sebastian,
The truth you speak doth lack some gentleness,
And time to speak it in.You rub the sore
When you should bring the plaster"
In these words,Gonzalo is criticizing what Sebastian has told Alonso.In these lines,Alonso's heart is the sore,made by the loss of his son.Gonzalo says that Sebastian is "rubbing the sore" meaning that Sebastian isn't helping Alonso overcome his loss.The "plaster" is the kind,compassionate and encouraging words spoken by Gonzalo and time needed to mend Alonso's bleeding heart.Gonzalo thinks that even though Sebastian spoke the truth,he should have said it gently.