To keep is simple, when the honey is first made it is in the clear form. Then the natural sugars in the honey react to each other over time and they slowly turn the honey thick. Some honey turns thick faster than other honey, all depending on what sort of flowers the bees have visited. If you want to make thick honey clear, then gentle warm the honey up by standing it in hot water until the crystals have desolved again.
The honey can be eaten either way, but thick honey is normally used for bread and toast and clear honey gets used in drinks and cooking alot more.
More Detailed, Honey is produced from nectar by, among other things, reducing the water content to <20%, and this is fone in the hive at about 35c. The bees will have removed the excess water to help preserve it against yeast fermentation for the winter stores. Yeast can only proliferate and spoil a product if there is enough moisture to be had from the product. There should be no surplus water in a ripened honey; just enough to keep the sugars in solution. As the honey cools when taken from the hive, whether in the comb, in your bucket or jar, it becomes 'super saturated' i.e. at lower temperatures there is not enough water to keep the sugars in solution. It is physically unstable. It stabilises itself by crystallising out (granulating or setting) some or all of the sugars. The principal sugars in honey are fructose and glucose and glucose is less soluble than fructose. Therefore honeys that are high in glucose will rapidly crystallise, such as Oil seed rape honey.