Genesis 12:18-20 meaning

Sarai's restoration to Abram came with the rebuke from Pharaoh, here is your wife, take her and go (v 19). We are not told how Pharaoh comes to understand it is God's hand and that Sarai is Abraham's wife. Once he comes to know that God is protecting Abram, Pharaoh returns Sarai and takes no revenge on him. Although it is not told to us here explicitly, it is likely God prevented Pharaoh from having sexual relations with Sarai. The same scenario occurs later in Genesis 20 and it is explicitly stated there that God prevented any sexual misconduct from occurring (Genesis 20:6),

So they escorted him away, with his wife and all that belonged to him (v 20), allowing them to keep all the wealth Abram had accumulated while in Egypt. They were escorted out of the country by Pharaoh's men probably to make sure they left. Abram was publicly humbled by the Pharaoh and expelled in disgrace. Abram and his household then returned to Bethel in Canaan. The story of Abram in Egypt foreshadows Israel's later slavery in Egypt where they will also be delivered by plagues and leave with great riches (Genesis 47:27; Exodus 7:14 - 11:10, 12:31-36).