11 The emphasis on sequence is clear because the form is the perfect tense with the vav consecutive. The use of the verb “to know” (יָדַע, yada’) underscores what was said with regard to 6:3. By the time the actual exodus took place, the Egyptians would have “known” the name Yahweh, probably hearing it more than they wished. But they will know—experience the truth of it—when Yahweh defeats them.
12 This is another anthropomorphism, parallel to the preceding. If God were to “put” (נָתַן, natan), “extend” (נָטָה, nata), or “reach out” (שָׁלַח, shalakh) his hand against them, they would be destroyed. Contrast Exod 24:11.

In other versions

The Egyptians shall know that I am the Lord, when I stretch out my hand against Egypt and bring out the people of Israel from among them.”

And the Egyptians will know that I am the Lord when I stretch out my hand against Egypt and bring the Israelites out of it.”

The Egyptians will know that I am the Lord when I stretch out my hand against Egypt and bring out the Israelites from among them.”

When I raise my powerful hand and bring out the Israelites, the Egyptians will know that I am the Lord.”

And the Egyptians will know that I am Yahweh when I stretch out my hand over Egypt and bring the Israelites out from their midst.”

And the Egyptians shall know that I am the Lord, when I stretch forth mine hand upon Egypt, and bring out the children of Israel from among them.

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