Abraham lied to Abimelech, God had mercy on both of them.
Genesis 20:1-6, 14-16 Abraham moved south to the Negev and lived for a while between Kadesh and Shur, and then he moved on to Gerar. While living there as a foreigner, 2 Abraham introduced his wife, Sarah, by saying, "She is my sister." So King Abimelech of Gerar sent for Sarah and had her brought to him at his palace.
3 But that night God came to Abimelech in a dream and told him, "You are a dead man, for that woman you have taken is already married!"
4 But Abimelech had not slept with her yet, so he said, "Lord, will you destroy an innocent nation? 5 Didn't Abraham tell me, 'She is my sister'? And she herself said, 'Yes, he is my brother.' I acted in complete innocence! My hands are clean."
6 In the dream God responded, "Yes, I know you are innocent. That's why I kept you from sinning against me, and why I did not let you touch her. 7 Now return the woman to her husband, and he will pray for you, for he is a prophet. Then you will live. But if you don't return her to him, you can be sure that you and all your people will die."
14 Then Abimelech took some of his sheep and goats, cattle, and male and female servants, and he presented them to Abraham. He also returned his wife, Sarah, to him.15 Then Abimelech said, "Look over my land and choose any place where you would like to live."16 And he said to Sarah, "Look, I am giving your 'brother' 1,000 pieces of silver in the presence of all these witnesses. This is to compensate you for any wrong I may have done to you. This will settle any claim against me, and your reputation is cleared."
Psalm 145:9 The LORD is good to all, and his mercy is over all that he has made.
It wasn't fair to Abimelech that Abraham put Sarah out there for him to consider as an addition to his harem. The Philistine king of Gerar was deceived into believing that Sarah was only Abraham's sister and so after he saw her good looks he decided that he wanted her.
Abraham wasn't being authentic that day, he was being as phony as a Pharisee, you know how deceptive the Pharisees were. Abraham was hiding the facts from the king for his own gain.
It would have been a disgrace if Abimelech had decided to sleep with the newest member of his harem on her first night. God intervened in this situation and kept Abimelech from being with Sarah and God gave him the truth about who Sarah was. God's mercy stopped the messy chain of events that could have occurred. Mercy was given to Abimelech as well as Abraham.
God shares his mercy with everybody, the "good" and the "bad", we all benefit from his goodness. The question that we have to ask ourselves is "Will the Lord show me mercy on judgement day?" I hope that you know the answer is yes.
On that final judgement day there will not be mercy for everybody as there was in this story, it will only be for those of us that believe that Jesus paid the death penalty for sin. The ultimate day to receive mercy is on the way, are you ready?