Genesis 20:2 And Abraham said of Sarah his wife, She is my sister: and Abimelech king of Gerar sent, and took Sarah.
For the second time Abraham is sojourning in a foreign land with his wife, Sarah, and for the second time he lies about Sarah. He said she was his sister. This was a half-truth since she was a half-sister, but the point of it was to deceive. However, that lie put Sarah in jeopardy, for Abimelech took her into his harem. Abraham had been called by God and given Covenant promises that will come to pass. Abraham believed God, but he also doubted His promise and could not fully trust in the Lord in this instance. He relied on human scheming and sin. The tension in Abraham builds: will Abraham’s developing faith mature? Will Sarah survive to bear the promised seed? The answer is Yes, but we are put in suspense.
We also believe God and trust Him for forgiveness and salvation, but unbelief lurks and we sometimes have doubts. God loves us so that He allows trials, temptations, doubts, and down times to come in order to grow and strengthen our faith, to be tested, to work out the salvation we have, and to learn by experience that God is still faithful and always good.