Reread lines 58-76 in scene 2. what does hamlet admire about horatio? how does shakespeare use horatio to develop the play's plot?

In Hamlet by William Shakespeare, Hamlet lets the audience know about the best features in his best friend Horatio in Act 3, scene 2:

Below are the lines referenced in your question and a short interpretation of Horatio's admirable qualities.

And could of men distinguish, her electionHath sealed thee for herself, for thou hast been—As one in suffering all that suffers nothing—A man that Fortune’s buffets and rewardsHast ta'en with equal thanks.
                                                                             [He's resilient]
And blessed are thoseWhose blood and judgment are so well commingled,That they are not a pipe for Fortune’s fingerTo sound what stop she please.
                                                          [He has good judgement]
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.—Something too much of this.—
       [He is a rational man who's not controlled by emotions]
There is a play tonight before the king.One scene of it comes near the circumstanceWhich I have told thee of my father’s death.I prithee, when thou seest that act afoot,Even with the very comment of thy soulObserve mine uncle. If his occulted guiltDo not itself unkennel in one speech,