In Act III, scene 2, Hamlet is giving advice to the players who are about to perform "The Murder of Gonzago". He says the purpose of drama is to imitate life. He has cautions the players not to be too "tame" or to "overdo" their actions because "the purpose of playing, whose end, both at the first and now, was/ and is, to hold, as 'twere, the mirror up to nature...".( III,ii,19-20) In other words, the purpose of acting and, therefore drama, is to come as close to reality as possible. A little later, he praises Horatio for being an "even" or not battered by his emotions. He says, Horatio, "thou art e'en as just a man
As e'er my conversation cop'd withal. ( III,ii,49-50)
Horatio is a little embarrassed by the compliment but Hamlet goes on to say,"Give me that man/ That is not passion's slave, and I will wear him/ In my heart's core, ay, in my heart of heart,/As I do thee."
( III,ii, 67-70) In other words, Horatio is not a slave to his emotions and that is what Hamlet admires in him.
Hamlet lectures the players on realism in acting and theatre. While speaking in general terms about the purpose of drama, he states it should be a mirror of the actual world. Drama's point has always been ("first and now") to show audiences what goodness ("virtue") really looks like and also to show what nastiness ("scorn") is really like, as well as to show the larger society what it is like ("the very age and body of time his form"). As he puts it:
For anything so overdone is from the purpose of playing, whose end, both at the first and now, was and is to hold, as ’twere, the mirror up to nature, to show virtue her own feature, scorn her own image, and the very age and body of the time his form and pressure.
Give me that manThat is not passion’s slave, and I will wear himIn my heart’s core, ay, in my heart of heart,As I do thee.