Moses and Aaron did so refers back to verse 2, which describes the procedure for speaking to the king. But they did as the LORD commanded also includes the specific commands recorded in the following section. This verse therefore functions both as a conclusion to what has been said and a preview statement of what will soon be described in detail.

The two clauses say almost the same thing, but the repetition adds emphasis. When they are combined as in Good News Translation, the emphasis is lacking. New English Bible brings out the emphasis better: “So Moses and Aaron did exactly as the LORD had commanded.” The implication is that Moses from now on obeyed without offering any more excuses.

Quoted with permission from Osborn, Noel D. and Hatton, Howard A. A Handbook on Exodus. (UBS Helps for Translators). New York: UBS, 1999. For this and other handbooks for translators see here .