Neal A. Maxwell
"The Lord in a revelation for John Whitmer spoke of that which was in the latter’s heart, which only the Lord and John Whitmer knew, witnessing that God was omniscient concerning the needs of that individual. (D&C 15:3.)
"Paul said to the saints at Corinth, ’And again, The Lord knoweth the thoughts of the wise, that they are vain.’ (1 Corinthians 3:20.) In the period just before the flood God saw not only the wickedness of man in the earth, but he saw also ‘every imagination of the thoughts’ of men’s hearts. (Genesis 6:5.) He knows ’the things that come into your mind.’ (Ezekiel 11:5.) Jesus himself said before we pray, ’Your father knoweth what things ye have need of.’ (Matthew 6:8.) Indeed, as Nephi said, ’God … knoweth all things, and there is not anything save he knows.’ (2 Nephi 9:20.)
“Hence omniscience is one of the characteristics of the living God. As we read in Helaman 9:41, ’Except he was a god he could not know of all things.‘ ’And now, behold, you have received a witness; for if I have told you things which no man knoweth have you not received a witness?’ (D&C 6:24.)” (Things As They Really Are, p. 22)