Robert frost is saying that when the reader first reads the poem in he beginning it should be playful and make the reader interested and grasp the topic, but by the end the poem should bring wisdom or a lesson. By the end of the poem the reader should have taken something out of the poem and learned something from it.
See the flying of the teacher,
I think she's angry at the kids on the bleachers.
Cat's personalities and dog's personalities are often considered calming to humans.
