I know is emphatic, and some translations try to bring this out: “I know well” (New English Bible); “Yet I know” (New Jewish Publication Society’s Tanakh); “I am well aware” (New Jerusalem Bible). Will not let you go is literally “will not permit you [plural] to go.”

Unless compelled by a mighty hand follows the Septuagint rather than the Hebrew Masoretic Text, as the footnote in Revised Standard Version explains. The meaning in Hebrew is ambiguous, “not even with a mighty hand.” The question hinges on whose hand is referred to. It could mean either human strength or the power of God. Die Bibel im heutigen Deutsch in fact understands it as a “power of the world.” However, since verse 20 clearly speaks of God’s power (“I will stretch out my hand”), most translations follow the meaning suggested by the Greek text. This may be expressed positively as in New Jewish Publication Society’s Tanakh, “Yet I know that the king of Egypt will let you go only because of a greater might.” Another way to express this is “I know that the king of Egypt won’t let you go until he discovers [or, realizes] that I am more powerful than he is.”

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 .