'Know the Truth' in the Bible

Then I wanted to know the truth of the fourth beast, which was different from all the others, very frightening, whose teeth were of iron, and his nails of bronze; who devoured, broke in pieces, and stamped the rest with his feet;

And you shall know the truth, and the truth shall make you free.

forbidding to marry, saying to abstain from foods which God has created to be received with thanksgiving by those who believe and know the truth.

I have not written to you because you do not know the truth, but because you know it, and know that no lie is of the truth.