Jesus didn't just declare that He knew Abraham. He declared that He is I AM. The entire Bible declares Jesus is God. From Genesis 1:1 - Revelation 22:21. As the Bible declares: Jesus is the Rock and God is the Rock. Jesus is God. The Jews knew exactly Who Jesus said He is.
http://www.christadelphians.com/biblebasics/d03godmanifestation.html
http://www.pickle-publishing.com/papers/angel-yahweh.htm