Abraham and Abimelek: Lies of Omission and Half-lies Are Still Lies

Abimelech rebuking Abraham by Wenceslaus Hollar

After Abraham was personally visited by angels and by Jesus, (Genesis 18:1-3, 14), and after Abraham personally asked for the LORD to protect his nephew Lot from destruction in Sodom, (Genesis 18:22-23), and after Abraham personally witnessed the destruction of four of the five Cities of the Plain (Genesis 19:28), despite having had another reassurance by God of His chosen plan involving Abraham (Genesis 15:6), thus knowing his God's sovereign power, holiness, and mercy, in the next chapter Abraham lied. And why? To help God out.
In Genesis 20:1, Abraham is journeying in King Abimelek's lands. ("toward the territory of the Negeb and lived between Kadesh and Shur; and he sojourned in Gerar." Gen 20:1). Abraham thought to himself that since the people in that area are not God-fearing, I am going to need to lie about my beautiful wife Sarah.
And Abraham said of Sarah his wife, “She is my sister.” And Abimelech king of Gerar sent and took Sarah. (Genesis 20:2).
Twenty-five years earlier, Abraham said that of his wife when he feared Pharaoh. Pulpit Commentary said of Abraham's lie then and in this chapter, that lying was "an ignoble expedient."
Did Abraham think God didn't know that the lands in the Negev were filled with pagans who did not fear God? Did Abraham think God needed to be helped out? Did Abraham not want to bother God with a prayer-petition for safety for his wife and himself? Or did Abraham just not trust God enough?
Let's look at what Abraham's lie did to himself and others. Then I'll look at the sovereignty of God and how He worked through Abraham's sinful lie.
Now, Sarah really was his sister, or half-sister to be specific. "she is indeed my sister, the daughter of my father though not the daughter of my mother, and she became my wife." (Genesis 20:12). So Abraham's lie was a half-truth. Alternately it can be called a lie of omission. It is still a lie. Lies we tell have effects upon the people who hear them. In this case, Abimelek went forward with an action that was based on faulty information, and he took Sarah. Then night God came to him in a dream with a message. And the message was not good.
"Behold, you are a dead man because of the woman whom you have taken, for she is a man’s wife." (Genesis 20:3b)
Thanks a lot, Abraham.
Now the King did plead with the LORD earnestly. I mean, Abimelek was told that she was not a wife. Here is where God's sovereignty over ALL FLESH comes in.
"Yes, I know that you have done this in the integrity of your heart, and it was I who kept you from sinning against me. Therefore I did not let you touch her." (Genesis 20:6)
God is sovereign and can and does control ALL that happens on earth and even within the hearts of men and allows or prevents certain actions. Example: God would not let Abimelek touch Sarah. Did God put a wall around Sarah or consign her to a room in chains far away from Abimelek? No. He invisibly ordained that Sarah would remain untouched and in His power He made that come to pass, even though the King, Sarah, and the entire household was not aware of His workings. This is Providence.
God told the King to release Sarah and not to touch her or the King would certainly die. Abimelek called all the servants together and told them all that had happened, and followed God's commands immediately. (So much for NOT being God-fearing, eh? Not that the King was a believer, but the king did recognize God's authority and His power, and submitted to it in this instance.)
Then the King severely rebuked Abraham.
"What have you done to us? And how have I sinned against you, that you have brought on me and my kingdom a great sin? You have done to me things that ought not to be done." (Genesis 20:9b-10).
That is the problem with lying. Not only did Abraham sin, not only did Abraham lead his wife into sin, but it caused the King to sin also, albeit unknowingly. He had a right to be angry. As did Pharaoh 25 years prior. Pulpit Commentary says of Abraham's current lie and the 25 year old lie,

Abraham should a second time have resorted to this ignoble expedient after the hazardous experience of Egypt and the richly-merited rebuke of Pharaoh, but more especially after the assurance he had lately received of his own acceptance before God (Genesis 15:6), and of Sarah's destiny to be the mother of the promised seed (Genesis 17:16), is well nigh unaccountable, and almost irreconcilable with any degree of faith and piety.

Of course we know Abraham was faithful and pious. (Hebrews 11:11). Our Bible is so great to show us the successes and the foibles and fumbles of the great men and women who are recounted in this record. We are all sinners, tending toward doing wrong most of the time, yet our God uses us again and again in His plan to move history forward to the end goal of displaying His glory to an unspotted Bride. Abraham was no different. But more gloriously, God is no different. He is totally sovereign over all that happens. After Abimelek gave Abraham 1000 pieces of silver, animals, and free passage through the land, he said you have been vindicated and this matter is concluded.
Just as God had promised Abimelek, (Genesis 20:7) Abraham then prayed to God on the King's behalf (Genesis 20:17). God opened the wombs of all the women in the house of Abimelek because he had closed them on behalf of Sarah. God is sovereign over wombs, minds, flesh, and events. He is also merciful, in sparing Abimelek, in not punishing Abraham, in protecting Sarah, and in allowing the females of the house of Abimelek to conceive babies once again.
Genesis 20 is a tremendous chapter on the sinfulness of man, of what lies do to people (even lies of omission). Imagine what Abimelek might have been thinking. 'Why would God pick THAT guy, he's a liar.' Do you want your witness on behalf of Holy God to be polluted by a legacy of lies?
The chapter is also a wonderful example of God's sovereignty and Providential outworking, and His mercies.
Gill's Exposition on Genesis 20:2-

And Abraham said of Sarah his wife, she is my sister,.... This he gave out in all conversation he came into, and said it to every one that asked who she was, which was little better than a lie; it at least was an equivocation and deception, and not at all justifiable, and tended to expose his wife's chastity, and discovered a distrust of divine Providence; the same infirmity be had given way to, and the same evil he had fallen into in Egypt, Genesis 12:11, and therefore was the more inexcusable now; good men not only fall into sin, but have their relapses:

BibleGateway's All the Men of the Bible explains of Abimelek:
THE MAN WHO REBUKED ANOTHER FOR LYING

Abimelech would have taken Sarah, Abraham’s wife, into his harem, but learning that she was the wife of another, returned her uninjured. Abraham appears here in a bad light. He deceived Abimelech, but when found out was justly rebuked by the God-restrained Abimelech. Certainly the righteous should rebuke the ungodly (1 Tim. 5:20), but how sad it is when the ungodly have just reason for rebuking the righteous. What a degradation it was for Abraham, then, to be rebuked by a heathen king!
Abraham sought to palliate his deception by claiming that Sarah was actually his half sister, daughter of the same father but not the same mother (Gen. 20:12, 16).
A lie if half a truth Is ever the worst of lies.
Abraham was the more blameworthy because he had done the same thing before (Gen. 12) and had suffered much in the same way as upon this occasion. How grateful Abimelech was for the dream warning him of his danger! The covenant made with Abraham is somewhat significant—
I. It was proposed by Abimelech who, although knowing how Abraham had failed God, yet saw how favored he was of God (Gen. 21:22).
II. It revealed certain distrust of Abraham. Abimelech requested Abraham not to be tempted to sin in such a direction again (Gen. 21:23).

Wow, a pagan praying for the righteous!
We faithful Christians sure do have relapses. We are redeemed by, governed by, supported by, sustained by, and provided for by a gracious and loving God. He knows all the details, He is calmly in control of all that happens. He even forgives our sins (like when we lie). We don't need to "help" God in His plans but we do need to submit to them. We need to remember that our actions and words affect other people. We need to have integrity in all that we do for Jesus (Colossians 3:17).
PS: trivia- did you know that Genesis 20 is the first time we read the word "prophet"? God said Abraham was His prophet. (Genesis 20:7). The Bible is so wonderful to read!