Generally speaking, when we come across a reference to angels in the Torah, we do not necessarily have to engage in an extensive "pshat" investigation. In most cases, the intention of the verse is to basically refer to God, perhaps with the added import that it is a relatively indirect action of God. The word "malakh" means "agent" and angels are heavenly agents for God, closely associated with Him.
In Parshat Mishpatim, however, we have a case where the immediate pshat of the reference to an angel is not to associate him with God, but to distinguish him from God. An action takes place with an angel, and because the angel is NOT God, certain consequences are in place. This forces us to pay much more attention to the pshat of what the angel is meant to signify, and why an action of an angel is different than one of God.
