So, Abram and Sarai went down to Egypt, and Abram decided to tell a little fib to better his situation. He knew that his wife was beautiful, and it seemed reasonable to him that Pharaoh would kill him so he could have Sarai.
It’s incredible to me that neither Abram nor Sarai told Pharaoh the truth. Apparently, their trust in God was pretty weak, even though the chapter starts with God’s promise that He is going to bless them and bring a great nation out of them.
Perhaps that promise was on Abram’s mind as he told Sarai, "Say you are my sister, so that I will be treated well for your sake and my life will be spared." (vs 13) Maybe Abram thought he was the reason Sarai couldn't get pregnant and have that "great nation." Sarai did what Abram said, and she was taken into Pharaoh’s palace, as he had the intention of making her his wife. Again, this was apparently okay with both Abram and Sarai.
But it wasn’t okay with God. God deals in truth and reality, and even when His ambassadors on this earth are less than truthful, God is never less than truthful! He always communicates truth, and He always knows how to communicate truth so we receive and understand the message.
Verse 17 says the Lord sent a "terrible plague" on Pharaoh’s household because of Sarai. At first, this doesn’t seem right, does it? After all, Pharaoh took Sarai into the palace because Abram and Sarai were dishonest about their marital status. Why would God punish Pharaoh with a plague because Abram and Sarai did something wrong?!
But then, right away, we see that the "plague" wasn’t a punishment. It was a message, because in the very next verse, Pharaoh summons Abram and asks him why he was dishonest. Pharaoh got the message! Abram and Sarai had pulled the wool over Pharaoh's eyes, but God wasn’t going to leave him in the dark!
Only God knows why it took a "plague" to communicate with Pharaoh. Perhaps, in Egyptian culture and folklore, there were certain rashes or marks that communicated certain things. Whatever it was, in this story, we see that it is God who communicates truth to us—in any way we are able to understand it. He loves to work through His agents on this earth, but He is certainly not limited by His agents on this earth, and He is certainly able and very willing to communicate His truth to us, no matter who we are, no matter what situation we’re in.