Honey has a natural tendancy to gradually crystalize over time, depending on the sugar content of the nectar foraged. Some nectars will cause honey to crystalize quicker than others, along with a variety of other contributing factors. To preserve the natural goodness in raw honey, you can place your jar in a pot of water on slow and low heat (just before a boil) and patiently wait for it to return to liquid. If you have a plastic bucket of honey, you should be able to also place in enough water that the two bottoms do not touch, and follow the same steps.