Minecraft wiki entry for Diamonds, associated text: The player can see the enchantment to be granted, and more enchantments may be granted on that pick, so if it says Fortune III, enchant it as soon as possible. Players don't need to worry if they don't have enough levels, the enchantment stays the same until it is used. Remember, the player needs thirty levels for a 30-level enchantment, but it costs only three. Choosing one of the lower tiers, it costs only 1 or 2 levels.