Priest Spells (PHB)

The spells of a priest, while sometimes having powers similar to those of the wizard, are quite different in their overall tone. The priest's role, more often than not, is as defender and guide for others. Thus, the majority of his spells work to aid others or provide some service to the community in which he lives. Few of his spells are truly offensive, but many can be used cleverly to protect or defend.
Like the wizard, the priest's level determines how many spells he retains. He must select these spells in advance, demonstrating his wisdom and far-sightedness by choosing those spells he thinks will be most useful in the trials that lurk ahead.
Unlike the wizard, the priest needs no spell book and does not roll to see if he learns spells. Priest spells are obtained in an entirely different manner. To obtain his spells, a priest must be faithful to the cause of his deity. If the priest feels confident in this (and most do), he can pray for his spells. Through prayer, the priest humbly and politely requests those spells he wishes to memorize. Under normal circumstances, these spells are then granted.
A priest's spell selection is limited by his level and by the different spheres of spells. (The spheres of influence, into which priest spells are divided, can be found under "Priests of a Specific Mythoi" in Chapter 3: Player Character Classes.) Within the major spheres of his deity, a priest can use any spell of a given level when he is able to cast spells of that level. Thus, a druid is able to cast any 2nd-level plant sphere spells when he is able to cast 2nd-level spells. For spells belonging to the minor spheres of the priest's deity, he can cast spells only up to 3rd level. The knowledge of what spells are available to the priest becomes instantly clear as soon as he advances in level. This, too, is bestowed by his deity.
Priests must pray to obtain spells, as they are requesting their abilities from some greater power, be it their deity or some intermediary agent of this power. The conditions for praying are identical to those needed for the wizard's studying. Clearly then, it behooves the priest to maintain himself in good standing with this power, through word and deed. Priests who slip in their duties, harbor indiscreet thoughts, or neglect their beliefs, find that their deity has an immediate method of redress. If the priest has failed in his duties, the deity can deny him spells as a clear message of dissatisfaction. For minor infractions, the deity can deny minor spells. Major failings result in the denial of major spells or, even worse, all spells. These can be regained if the character immediately begins to make amends for his errors. Perhaps the character only needs to be a little more vigilant, in the case of a minor fault. A serious transgression could require special service, such as a quest or some great sacrifice of goods. These are things your DM will decide, should your character veer from the straight and narrow path of his religion.
Finally, your DM may rule that not all deities are equal, so that those of lesser power are unable to grant certain spells. If this optional rule is used, powers of demi-god status can only grant spells up to the 5th spell level. Lesser deities can grant 6th-level spells, while the greater deities have all spell levels available to them. You should inquire about this at the time you create your character (and decide which deity he worships), to prevent any unwelcome surprises later on.