In the latter part of the parsha (Torah portion), post-Matan Torah (after the giving of the Torah) and after the "mishpatim" (laws) are given over, Hashem (G-d) mentions sending a "malach" (angel) to lead Am Yisrael (the nation of Israel), and promising prosperity through adherence to commandments.

Contrastingly, after the Golden Calf incident, Hashem wants to punish Am Yisrael by sending a "malach" to lead the way instead of Him, and the notion of an angel leading the way leads to outcry by Am Yisrael.

What's the difference? Why does the mention of an angel evoke varied responses? What is this "malach" about? What is a "malach" about??