The standard arguments for God's existence — even assuming that they worked — do not support the above claims. For example, design arguments at best conclude that some intelligent being is responsible for the characteristics found in the universe (or for some of these characteristics). They don't say that this being is all-powerful or all-good; they don't even show that this being created the universe out of nothing (she might only have rearranged previously existing matter), or that this being still exists. Nor do they show that monotheism is more likely than polytheism. Cosmological arguments fare even worse: at best, they show that there is some ultimate cause that is itself uncaused, or that necessarily exists. But by themselves, these arguments do not support the idea that this ultimate cause is an intelligent being, much less that it is a perfectly just and benevolent heavenly father, or one who has any of the other properties claimed by theists.
Then there is what one might call the argument from scripture: the Bible, it is said, shows that God is at least to a great extent as described above. However, the Bible at most only suggests this. It says, for instance, that “with God, all things are possible.” But that is rather vague, and can be interpreted in more than one way. True, if taken at face value, it says God can do anything; but it can also be read more poetically as a suggestion to put one's faith in the very powerful — though not necessarily all-powerful — creator being. And there are other passages in the Bible that if taken at face value are incompatible with God being omnipotent. (The Bible does at least state pretty clearly that God is male. But that's the most ridiculous of the divine properties that believers insist on.)
There are also, of course, the ontological arguments, and those do say that God is omnipotent, perfectly good, and more. But hardly anyone accepts ontological arguments. When they first encounter Anselm's “proof,” most theists suspect that some trick is involved, and rightly so.
It seems clear that the real reason theists accept most of these claims about God is because that is what they want to believe. In the entry on omniscience in The Blackwell Companion to the Philosophy of Religion, George Mavrodes mentions three reasons, besides the Anselmian “perfect-God” theology, why someone might claim God is all-knowing. First, there are biblical passages that “suggest a very wide scope for divine knowledge.” (This has exactly the same problem as the ones used to support belief in an omnipotent God. A “very wide scope” isn't necessarily an all-encompassing one. Plus, there are biblical passages that suggest God isn't all-knowing.) Then there is “the conviction that without an appeal to omniscience one could not maintain a full confidence in God's ability to achieve His purposes in the world.” Finally, there is the idea that God is a being fully worthy or worship, and only a perfect being qualifies as such.
These last two reasons, however, translate to “I believe God is all-knowing for otherwise I wouldn't have as strong as possible a reason for putting my faith in this being.” And if that's a good reason for believing God is all-knowing, or has any of his other commonly-claimed properties, then we might as well believe that carts can pull horses.
[Originally published at Debunking Christianity]