"To know someone" is used throughout the book of Genesis in the King James translation as a euphemism for sex. It's pretty obvious.

"And they called unto Lot, and said unto him, Where are the men which came in to thee this night? bring them out unto us, that we may know them.

6 And Lot went out at the door unto them, and shut the door after him,

7 And said, I pray you, brethren, do not so wickedly.

8 Behold now, I have two daughters which have not known man; let me, I pray you, bring them out unto you, and do ye to them as is good in your eyes: only unto these men do nothing; for therefore came they under the shadow of my roof."

By context it's clear that the men of Sodom had sexual motivations. Now perhaps you could argue that the angels were beautiful beings and they weren't gay or whatever. I don't think the bible is particularly clear on this point though it is heavily implied.

Compare the usage to Genesis.

"And Adam knew Eve his wife; and she conceived, and bare Cain, and said, I have gotten a man from the Lord."

"And Adam knew his wife again; and she bare a son, and called his name Seth: For God, said she, hath appointed me another seed instead of Abel, whom Cain slew."

Basically you can just replace the word know with the word fuck in these cases.