Why is the word "work" spelled with an "o"? I can't find the answer anywhere. I know it comes from Old English "weorc" but I can not find how it came to be spelled "work" instead of "werk".
Why are worship, world, worse, worm, word, worry, worth all spelled with "o"s? There was a sound change in many words beginning "wor" at some point after English spelling became fixed. When Shakespeare wrote
I think good thoughts whilst other write good words,
And like unletter'd clerk still cry 'Amen'
To every hymn that able spirit affords
In polish'd form of well-refined pen,
it rhymed. He also rhymes worth with forth. However, he rhymes worse with curse, so presumably worse was already pronounced the modern way; either the sound change had already happened or it had acquired its modern pronunciations for other reasons.
English pronunciation is often difficult to decode from orthography (correct spelling). Spelling relates more closely to etymology (word origin) and word history.
The letter r operates as a quasi-vowel, in that it influences the sound of the vowel that appears immediately before it.
Consider another rhyme with the vowel "O":
With one you can run,
with two you can go,
but when you've got three you must 'bide where you be.
This saying refers to a mother and the number of children she has. One rhymes with run, and three with be, so it is probable that this saying came about at a time when two rhymed with go. If that is not so, the saying is still a good illustration of the variety of "o" sounds.
I tread somewhere that when Caxton and others first put words into print they spelled them according to the way they were pronounced in that part of England they came from. Even now the pronunciation of the language is not standardized. That is why spelling is such a horror for some kids. Efforts to standardize spelling by people such as GBS have not succeeded.