Valar and Maia abilities?

[Zigûr]

Originally Posted by Inziladun

Well, I would clarify that idea to say that the Valar had great difficulty detecting deception because that act was in itself negative.

We can also observe these remarks from the second part of "Notes on motives in the Silmarillion" (Section VII "Myths Transformed" from Morgoth's Ring):
"No one, not even one of the Valar, can read the mind other other 'equal beings': that is one cannot 'see' them or comprehend them fully and directly by simple inspection."

Regarding the powers and abilities of the Valar, we might also take note of this comment from Section VI of "Myths Transformed" regarding Melkor:
"He was to make/devise/begin; Manwë (a little less great) was to improve, carry out, complete." Before his descent into evil, Melkor was intended by Eru as an initiator. We can see how this was corrupted into impatience, and in Morgoth's own hierarchy Sauron took on a role similar to that which Eru intended for Manwë, completing projects Morgoth could not "in the furious haste of his malice."