How does Alsemero's opening speech in Act I of "The Changeling" relate to a variety of areas throughout the play?
I'm not sure about a variety of areas, but one key part of his speech is his desire to wed Beatrice, and his assurance that he will do so.
There is great irony in Alsmero's speech. Firstly due to the fact he met Beatrice in a church and therefore believe's this to be a good omen. Yet later we see this meeting causes a string of sinful events.... this may also have connotations for the catholic church as the play is set in catholic spain and at this time the religion itself waas demonised. Alsmero also states that he 'love[s] her beauties to the holy purpose' suggesting all his feeling for her is based merely upon her appearance again demonstrating how he is opporating on an animalistic or sensory level within the jacobean notion of the soul; this is a state close to madness. You should also note that many problems occur due to misguided perceptions and the characters having too much faith in what their eyes show them (I think Beatrice states something along the lines of 'my troubles start at mine eyes' and 'our eyes are sentinals unto our judgements')