I have done this before and could not find a simple way to do it.
You can sort in Word so no need to import the text into Excel.
First you need to convert your body of text into one word per line. Use "Find and Replace" (press CTRL+H) and replace all spaces with a paragraph break.
Remove any punctuation the same way - eg search for full stops and replace with nothing.
You will probably end up with some extra blank lines in the result. You could try to remove all these by searching and replacing incidences of 2 paragraph marks with only 1. However, if you simply select all the text and then use Table > Sort to sort all the lines into alphabetical order, all the blank lines will end up together anyway and you can delete them then.
If you wanted to import the text into Excel to end up with one word per cell, simply select all the text (CTRL+A) in your one-word-per-line Word document, copy it (CTRL+C), open Excel or switch to it and paste (CTRL+V) the text into your spreadsheet.
There is also a concordance feature in Word which would enable you to index your original text document (if you keep a copy) by using the sorted word order document (edited so each word only occurs once) as the source file enabling Word to generate a concordance which will tell you on which page each word in the source file occurs.
HTH