The word in the Hebrew that is there translated into the English know, is yada (transliterated) and it has a wide variety of application and one of which is to lie by man, which the translators chose to interpret by the English word know, or in this case, by the past tense, knew. Now, what this does is it adds intimacy to the knowledge of God. It is not just something from which we are detached, but it adds to the knowing God the fact of being close to Him within a relationship. So it is not merely being acquainted. I think today we would probably say something that, it is like we're inside of His head. We know Him inside and out in a way that we are just beginning to understand.
The corresponding Greek word to the Hebrew yada is ginosko. Incidentally, this is exactly the same word that is translated know in John 17:3, and so it is used in the Greek, in the English, and in the Hebrew all in the same way.
The wording here, acquired a man from God suggests Eve thought Cain was the fulfillment of God's Messianic prophecy found in Genesis 3:15. There is further evidence that she could have had this on her mind in Genesis 4:25, which records the birth of Seth when she states, for God has appointed another seed for me. So it appears there is a good chance Cain was raised with a bit of a messiah complex and saw himself as far superior to his little brother. And we could recall Christ's words in Luke 22:26, Who was greater in the kingdom? Let him be as the younger. It is kind of an interesting tie-in. And if we tied into Jude 11,
