Some clerics devote themselves not to a god but to a cause or a
source of divine power. These characters wield magic the way clerics
devoted to individual gods do, but they are not associated with any
religious institution or any particular practice of worship. A cleric
devoted to good and law, for example, may be on friendly terms with
the clerics of lawful and good deities and may extol the virtues of a
good and lawful life, but he is not a functionary in a church
hierarchy.

All clerics in Faerûn serve a patron deity (In fact, most people in Faerûn choose a deity as their patron.) It is simply impossible for a person to gain divine powers (such as divine spells) without one. You
may not have more than one patron deity at a time, although it is possible
to change your patron deity if you have a change of heart. You
cannot multiclass into another class that requires a patron deity unless
your previous patron deity is an acceptable choice for the new class.
For example, you cannot multiclass as a druid unless your patron deity
is a nature deity (since all druids have nature deities as patron deities).
You may also bypass this restriction by abandoning your old deity outright
(see Changing Deities in Chapter 5: Deities). See the Religion section
of this chapter for more information on patron deities.

Because I'm lazy and don't want to look it up.....what is a favored soul?

In layman's terms? A cleric that uses charisma instead of wisdom.

Plus they still use Wisdom for DC calculation, but Charisma for the spell level. Or vice versa. I am not that sure.

Would it be possible for a favoured soul to be chosen against her will, and thus cursed to serve the being that chose her, much as she might try not to do so?

Correct.

Unlikely. I would say it would be comparable to having sorcerous potential. Not all with magical blood put effort into using it and becoming sorcerers.

The faithless are those who defiantly denied any faith or only gave lip service to the gods. The false are those who betrayed a faith they actually believed in and made a personal commitment to. All judged faithless receive the same punishment; they form a living wall around the city.

That's a shame. A favoured soul that actively opposes his deity, yet accidentally advances the cause of his deity through his every major action, would be an interesting concept, I think.

"are not able to devote themselves to a cause or a divine source other than their deity"

Unlike clerics, favored souls are not able
to devote themselves to a cause or a
source of divine power instead
of a deity. (pg. 7)

Can I make a Favoured Soul PC named Jeasus?

As an interesting sort of sidenote to this discussion, if anyone has the Book of Elder Evils, check out Sertous. A very nice twist on the "no gods but men" thing.

Couldn't find this on the interwebs. Is it a character name or a class?

But as a general rule, atheism is a bad choice in FR.

Seriously. It's not as badass to be atheist in world where the gods come down every so often and shake hands/kiss babies/make babies. I find it rather silly, especially when you the knowledge of what will happen to you after death is rather easily accessible to anyone in the adventuring field.

Yet in spreading these words, Avamerin unwittingly
released a great secret. Scholars and priests puzzled over
Sertrous’s dying words and made an incredible discovery:
One need not worship a god to gain the power of divine
magic. Rather than worship a god, a cleric could worship
an ideal and gain the same reward. He could worship the
mountains, or the sky, or the act of war, or himself. He
could even worship a slain obyrith lord. Avamerin saw
this plague of godless priests thrive and was powerless to
stop it. The solar realized his error, and when he confessed
to his lord, he was stripped of his rank and reduced to a
planetar’s status.
Enraged, Avamerin cast aside his servitude and stole
Sertrous’s head, claiming that the dead demon was wiser
than the gods. The gods recoiled and took from Avamerin
his beauty. If he would ascribe such value to a serpent’s
words, he would be one with them. The gods gave him the
visage of a snake and banished him from heaven. Yet the
damage had been done. The angel became the first heretic,
and he devoted the rest of his existence to serving the one
who had opened his eyes. In time, the devotion of Avamerin
and those he recruited to his Vanguard would be enough
to restore Sertrous to life and prove what the fallen angel
had come to believe was the truth beyond the lies of faith.

It's neat. But again, Forgotten Realms overrides things like that. Worshiping ideals doesn't net you anything, in terms of divine. Either worship a god, one of his aspects, or steal it from him, alive or dead.