Midrash Rabbah Ruth on YHVH and His People Israel

"Rabbi Shim'on bar Yochai taught: 'God, your God am I' (Psalms 50:7). God is saying here, 'In actuality, I am known as God (Elohim) to all the world's inhabitants, but I have designated My Name (YHVH) specifically only in connection with My people Israel; for I am not called "the God of the nations", but only "the God of Israel".'"

-- Midrash Rabbah, Ruth 1.1