Why do cooking instructions for jams and jellies tell you to add sugar to boiling fruit

[spaghetti arms]

the sugar is to sweeten. the boiling is to make sure the sugar and the pectin dissolve thoroughly before jarring.

 

[Jessica]

and pectin mix? Why do cooking instructions for jams and jellies tell you to add sugar to boiling fruit and pectin mix and then boil for a certain time before poiring into jars and sealing them?