Is this usage of 'the' acceptable?

Hi,

Let me jot down few things to set the context.

(Pretend that I am making a speach about my friend to the people in the auditorium.)

Hi, Let me tell you about my poor friend John and his family. They work 16 hours a day in the field and barely get by, but John has his eyes on greater things and hopes to go to college and get a job that will pay well. 

Friends, here in this auditorium, the change is coming and will come for John and his family and the change that comes will be good and will bring along situational changes where they will be blessed with no want of  material goods.

Praise the Lord, indeed.

My question:

Is the underlined 'the' correctly used in that the context of the speech allows the people in the auditorium to think of the same change which is the only change that will bring the situational changes for the poor friend of mine and thus, the usage is correct eventhough 'the' is used for the first time and the writing doesn't show the specificity explicitly?     

Thank you, CalifJim.

(Note: The quoted content may contain some unintentional typing mistakes.) 

In the post titled "Articles: 'in a world' vs. 'in the world'", How2die wrote this (also quoting the following that was part of his inquiry):

IN THOSE parts of the planet that might nonce have been described as "Christendom", this week marks the season of peace on Earth and goodwill towards men. A nice idea in a world more usually thought of as seasoned by the survival of the fittest. (from Economist.com)

I think, How2die  then went on to ask the question:

I was just wondering if anyone could explain why 'world' is used here with the indefinite article rather than with the definite one. 'A world' has been already implicitly specified in the first sentence since we have references to the planet and Earth. Furthermore, in the second sentence we also imply that we know which world we are talking about: notice the reference to thoughts and seasoning.

For his post, I think YOU kindly provided this among other things in your response.

In the case at hand, we have, more awkwardly expressed to show the pattern.

"This week marks the season of peace on Earth. This is a nice idea (in this world). This world is a world thought of as seasoned by the survival of the fittest"   

(To lead to my question) 

Here, the correlation between "Earth" and "This world" isn't clear to me although the case could be made in support of the existence of it. What I am trying to ask you through all this is "What is the difference between my original post and the post of How2die?" Did you buy his very good argument that 'A world' has been already implicitly specified in the first sentence of his since they have references to the planet and Earth? Partially basing his argument on that, I think, he has argued for the use of the definite article 'the'. Do you feel that a definite article, not an indefinite article, should be there for the phrase "in a world"? Or for that matter, did you comment on that?    

Hope for the answer.