What does Exodus 3:20 mean?

God has just delivered a message to Moses, which is to be given to the elders of Israel. Part of the message is a command to confront Egypt's king—the Pharaoh—and request a three-day leave for the Hebrews to worship God. This request, says God, will be refused, since Egypt will never relax its grip on their slaves without coercion.

In response, and to free Israel, God says He will "stretch out [His] hand" against the nation of Egypt. This was a common way for Moses to describe God's judgment (Exodus 7:5). This phrase is used often in the Old Testament, even outside of the books of Moses (Jeremiah 6:12; 51:25; Ezekiel 6:14; 14:9, 13; 25:13, 16; 35:3; Zephaniah 1:4). The idea of "striking" in judgment also recurs in Exodus. God "strikes" the Nile to turn it to blood (Exodus 7:17). He instructs Aaron to "strike the dust" to send gnats into the land of Egypt (Exodus 8:16). God also "strikes" the firstborn sons and animals in the tenth plague (Exodus 12:12, 13, 23 twice).

God refers to His upcoming plagues as "wonders." He later mentions "signs and wonders" in Exodus 7:3. God talks about His "wonders" being multiplied in Exodus 11:9, and Exodus 11:10 talks about Moses and Aaron performing "wonders" before Pharaoh. In Exodus 15:11 Moses and the people praise God for His "wonders.". Moses again returns to the theme of "wonders" in Deuteronomy, mentioning God's many wonders on six occasions (Deuteronomy 4:34; 6:22; 7:19; 26:8; 29:3; 34:11). These wonders would continue in the life of Israel in Joshua's time (Joshua 3:5), and God's many wonders would be praised throughout Scripture (Psalm 77:11, 14; 78:4, 11, 12).

As in the Gospel of John, the purpose of these miracles is to prove God's message, and His messenger, are true (John 20:30–31).