What does the word "right" mean in "whatever is, is right"?

I could guess.

" Epistle I concerns itself with the nature of man and with his place in the universe; Epistle II, with man as an individual; Epistle III, with man in relation to human society, to the political and social hierarchies; and Epistle IV, with man's pursuit of happiness in this world. An Essay on Man was a controversial work in Pope's day, praised by some and criticized by others, primarily because it appeared to contemporary critics that its emphasis, in spite of its themes, was primarily poetic and not, strictly speaking, philosophical in any really coherent sense: Dr. Johnson, never one to mince words, and possessed, in any case, of views upon the subject which differed materially from those which Pope had set forth, noted dryly (in what is surely one of the most back-handed literary compliments of all time) that "Never were penury of knowledge and vulgarity of sentiment so happily disguised." It is a subtler work, however, than perhaps Johnson realized: G. Wilson Knight has made the perceptive comment that the poem is not a "static scheme" but a "living organism," (like Twickenham) and that it must be understood as such.

Considered as a whole, the Essay on Man is an affirmative poem of faith: life seems chaotic and patternless to man when he is in the midst of it, but is in fact a coherent portion of a divinely ordered plan. In Pope's world God exists, and he is benificent: his universe is an ordered place. The limited intellect of man can perceive only a tiny portion of this order, and can experience only partial truths, and hence must rely on hope, which leads to faith. Man must be cognizant of his rather insignificant position in the grand scheme of things: those things which he covets most — riches, power, fame — prove to be worthless in the greater context of which he is only dimly aware. In his place, it is man's duty to strive to be good, even if he is doomed, because of his inherent frailty, to fail in his attempt. "

I think it means, "Whatever exists, was meant to be."

What? No... Beliefs like taste can never be truly wrong, misguided maybe. God's plan may be true, it may not.. ultimately it's an opinion. You either believe something or you don't.
2+2=4. Is right? It's scientifically correct.
How about 2+2=5? If I believe it to be correct, there's not much you can to dissuade me, but tell me the truth or your version of the truth and explain why my answer is wrong. If I still choose to believe 5 is the right answer - c'est la vie, I'm wrong in your eyes.
Since none of us will ever truly know the truth about god, unlike science or proven theories that are described as an absolute or provable.
A persons religious beliefs may be correct for them, but wrong for you. Nothing about religion is an absolute, unless the believer believes it is so. Yet, it still a belief and not an absolute till proven, and god still remain elusive.
Nothing about what was said before or in this reply has anything to do with destruction. However, if there was a war and the red team won and church goers believed that this was god's plan, who are we to argue. To the victor goes the spoils...
I might think they're full of crap, but that's my opinion, not the word of god or an absolute. Was this god's plan? Who knows?? but to the believers it will always be so.
There is a similar saying in Islam - it's the will of Allah.
It basically comes down to, you, the believer thinking, knowing in their heart of hearts, that god, in his/her infinite wisdom, can see the whole picture and while his/her plan may seem incomprehensible to you, the mere mortal, you have to/must believe that s/he knows best. In other words, Faith.