Observation: First, this is an incredible witness to the sovereignty to God. One may say that it is acceptable for God to control a man's actions for a "good thing" such as protecting the purity and dignity of a woman, and yet God has in fact here broken into the "free will" of a man and somehow restricted his actions.
Second, Abimelech, the king of Gerar recognized the Almighty God, walked in integrity, and called his nation "righteous". God agreed with those claims. This is yet another instance of God actively witnessing of His presence and Lordship to people outside the chosen line of the patriarchs through which Jesus came. No one, no one who has ever lived or who ever will live has any right to accuse God of unfairness when He comes for judgment on the hidden day of His choosing. Every person who ever existed has enough of a witness to respond to the testimony all around us that cries out to the existence of God, His deity and His goodness. Our very existence is unexplainable, though science tries, ad we are dependant daily on that which He provides. Furthermore, He has left His word which men and women are commanded to heed. Even Abimelech, regardless of his present innocent, was given commands to respond to - take action - obey! the word of God (vs 7).
Application: Consider well what God has revealed to me, and then respond! (see John 14:15, John 15:14, and Mark 4:24-25 among others)
Prayer: Father, lead me not into temptation, but deliver me from evil. And please teach me to employ my will to obey every word You have revealed to me. For in keeping Your word there is great reward, and truly it is sweeter than honey and the honeycomb to my soul. Your words are pure, true and unbreakable. I love you for revealing Yourself to me! Amen.