Take for example a Deity with 20 levels of Cleric. This deity may cast all cleric spells, all ranger spells and all her domain spells spontaneously - up to her daily limit of available cleric spell slots.
If this deity had levels in Druid or Paladin, he could also cast spells from these spell lists spontaneously as cleric spells (and as paladin or druid as well).
If a deity with for example 20 levels of wizard has the salient divine abilities Arcane Mastery and Spontaneous Wizard Spells, he could cast all wizard spells spontaneously, up to his daily limit of available wizard spell slots.
Example: Clr20/Wiz20/Pal10
Domains: Law, Good, Knowledge
Extra Domains: Healing
Salient Divine Abities: Arcane Mastery, Spontaneous Wizard Spells, Divine Spellcasting...
Abilities: Int 46, Wis 34
Cleric Spells/Day (Levels 0-12): 6/9/9/9/9/8/7/7/7/6/2/2/2
Wizard Spells/Day (Levels 0-18): 4/9/9/8/8/8/8/7/7/7/4/3/3/3/3/2/2/2/2
Paladin Spells/Day (Levels 1-2): 4/4
This deity can sponaneously cast all cleric, ranger, paladin, Law, Good, Knowledge and Healing spells, up to his daily limit of cleric spells per day and to her daily limit of paladin spells per day.
This deity can also sponaneously cast any wizard spell, up to his daily limit of wizard spells per day.
Quite godlike, huh?