As an agnostic I am certain of two things, the existence of God, and the inability of human religions to understand his will.
Two thoughts: 1. Agnosticism, by definition, lacks certainty. Therefore when an agnostic becomes certain of the existence of God, he is no longer an agnostic. He may, however, be a believer in God and be agnostic about the truth of a particular religion.
2. Key phrase: "human religions." If there is one that isn't human, but divinely revealed, then it is possible for some people, at least to a degree, to understand God's will because God has revealed it.
Steve.
"I was a deerhunter long before I was a man." ~Gene Wensel's Come November (2000) "A vote is like a rifle; its usefulness depends upon the character of the user." ~Theodore Roosevelt