You have to know that polar molecules are soluble in polar solvents.
Since glucose is polar, it dissolves.
Now do you know why do polar molecules dissolve? That's because water has a slight negative charge (
) at the oxygen atom and a slight positive charge (
) between the hydrogen atoms. The water molecules are attracted to the glucose polar parts (positive part of water to the negative part of glucose and vice versa) and can therefore separate glucose molecules from the other glucose molecules, hence dissolving.
Hope it helped! :)