The most important goal of a speaker's opening lines is to

The most important goal of a speaker's opening lines is to first and foremost, catch the audience's attention. A speaker is not a speaker without an audience and it is his role to garner the attention in order to deliver his speech well. There are numerous techniques to do this, such as starting with a quote for example.

Hamlet's fourth soliloquy is probably his most famous one - "to be or not to be."it is rather different from his previous soliloquies because now he is contemplating something that didn't come up before - suicide. he is thinking whether it is worth it to fight to find his father's murderer when in the end all of them are going to die, so why not die sooner than later. he is contemplating if he should go on fighting or just kill himself and end it all, which is why this soliloquy in particular is rather depressing, hesitant, and gives a deeper insight into hamlet's madness.