There is a common misconception that crystallised honey has gone off. It’s hasn’t, it’s still good, so don’t throw it out!
Crystallisation is often referred to as granulation, it is when your honey turns from a liquid state into a semi-solid state. It is an entirely natural process and the rate at which your honey will crystallize varies honey to honey depending on the nectar source as well as the temperature, the ratio of fructose to glucose in the honey as well as the amount of pollen in the honey itself.
Commercial honey is often heat treated and fine filtered (which removes much of the pollen) to create a shelf stable honey that looks clearer and brighter, making it easier to blend with many different types of honey. Commercial honey often does not crystallise as quickly as honey from your local beekeeper. This is because the natural state of the honey has been altered to create a more commercial product. In contrast, you will find that pure, raw (unheated) and single source honey (that is not blended) will have a natural tendency to crystallise over time.
Crystallisation of honey does not affect the honey except for the colour and texture, so there is no need to throw it out. Crystallised honey is great in tea, spread on toast and adding to glazes for meat.
If you really can’t live with crystallised honey, then you can revive it back to a more liquid state by warming it gently in warm water. However do this slowly as overheating your honey will reduce its quality (by destroying its enzymes and reducing the delicate flavours and aromas).
If you want the best honey, buy raw, single origin honey which is traceable back to a beekeeper. It will crystallise eventually, however it is nothing to worry about. Honey can keep for many years without spoiling. Keep eating your honey, and learn to love it even when it’s crystallised!